IPCS INCHEM Home


    INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

    WORLD HEALTH ORGANIZATION





    TOXICOLOGICAL EVALUATION OF CERTAIN
    VETERINARY DRUG RESIDUES IN FOOD



    WHO FOOD ADDITIVES SERIES: 43





    Prepared by the Fifty-second meeting of the Joint FAO/WHO
    Expert Committee on Food Additives (JECFA)





    World Health Organization, Geneva, 2000
    IPCS - International Programme on Chemical Safety


    PORCINE SOMATOTROPIN

    First draft prepared by Preben Olsen

    Institute of Food Safety and Toxicology
    Danish Veterinary and Food Administration
    Copenhagen, Denmark

    Explanation
         Biological data
              Biochemical aspects
                   Absorption, distribution, and excretion
              Biotransformation
                   Effects on enzymes and other biochemical processes
              Toxicological studies
                   Acute toxicity
                   Short-term studies of toxicity
                   Reproductive toxicity
              Observations in humans
              Short-term toxicity of insulin-like growth factor
    Comments
    Evaluation
    Acknowledgement
    References

    1.  EXPLANATION

         Studies of three analogues of native porcine somatotropin (pST)
    that are produced by recombinant DNA techniques1 were reviewed for
    the first time by the Committee. Their use in animal production is to
    increase body-weight gain and feed efficiency and to affect carcass
    composition by producing pigs with more protein and less fat. The
    Committee considered only the safety for consumers of foods containing
    residues of recombinant porcine somatotropin (rpST) in this
    toxicological monograph.

    2.  BIOLOGICAL DATA

    2.1  Biochemical aspects

         pST, a single polypeptide chain of 190 amino acids, exists as
    three variants comprising 183, 191, or 193 amino acids. Reporcin has
    the amino acid methionine at the N-terminus (Henry, 1998), and in
    Grolene the first seven amino acids are deleted from the N-terminus
    (Sargent, 1998). Somagrepor has an additional three amino acids at the
    N-terminus at position 1 and four substitutions in the amino acid
    sequence at positions 6, 11, 183, and 191 (Cyanamide, 1992).

                       

    1  Grolene(R), Reporcin(R), and Somagrepor(R); common names
         were not available for these products.

         Although the molecular structure of recombinant products differs
    from native pST, it is appropriate to consider them together in this
    evaluation because they act by binding with high affinity to the pST
    receptor. 

         pST showed cross-species bioactivity  in vivo in rats
    (GhiasUddin et al., 1984a) and dogs (Prahalada et al., 1998) but not
    in hypophysectomized monkeys (Knobil & Greep, 1959). Although the
    homology in amino acid sequence between porcine and human somatotropin
    is about 66% (Wallis, 1975), differences in bioactivity are seen which
    are due to the complementary molecular structures and their
    non-covalent binding to highly specific receptors on the membranes of
    target cells (Hughes & Friesen, 1985). Accordingly, pST did not
    inhibit 125I-human somatotropin in liver tissue  in vitro, indicating
    that pST does not bind to human somatotropin receptors (Carr &
    Friesen, 1976).

         Recombinant and native pST are biologically equivalent and have
    comparable activity  in vitro for specific inhibition of 125I-pST in
    the liver microsomal membrane fraction of pigs (Chung & Etherton,
    1986) and rabbits (Martin & Yunger, 1989). In comparative studies  in
    vivo, growth was stimulated in hypophysectomized rats treated
    subcutaneously with rpST or pST for nine days (GhiasUddin & Wilbur,
    1984a; GhiasUddin et al., 1984b) or for 10 days (Biroc, 1992) and
    growth performance, measured by weight gain, feed efficiency, and
    carcass composition, was improved in pigs treated with daily
    injections of rpST or pST for 77 days (Evock et al., 1988) or for up
    to 50 days (Eager, 1992).

    2.1.1  Absorption, distribution, and excretion

         As pST is a protein, it is likely to be degraded by digestive
    enzymes in the gastrointestinal tract (Nixon & Mawer, 1970) and has no
    activity when given orally. Oral administration of excessive rpST to
    rats for 15 days did not result in a detectable increase in serum
    rpST, measured by radioimmuno-assay (GhiasUddin & Bailey, 1988), and
    no effect was observed on key clinical and biochemical parameters. In
    contrast, these parameters were affected when rpST was given
    parentally (GhiasUddin & Bailey, 1988; GhiasUddin, 1989). Studies with
    the related bovine somatotropin showed ready cleavage by digestive
    enzymes  in vitro (Annex 1, reference 105), although proteolytic
    fragments had no biological activity (Hammond et al., 1990). 

         The serum concentrations of rpST in rats after intramuscular
    injection of 10 mg/kg bw were determined by radioimmunoassay at
    various times between 4 and 60 h, although the results at 4 h were
    discounted because of inaccurate determination. The serum
    concentration of 566 ng/ml at 6 h decreased gradually and after 60 h
    reached the background level of 10 ng/ml measured in control rats. The
    radioimmunoassay used showed 17% cross-reactivity with rat
    somatotropin (Martin, 1989). The biological half-life of rpST in rats
    could not be determined (Illi, 1989).

         In a study in pigs treated with radiolabelled 125I-pST or
    125I-rpST, the mean half-lives were 4 min for the fast phase for both
    compounds and 38 min for the slow phase for pST and 49 min for rpST
    (GhiasUddin, 1988a).

         The time course of serum somatotropin concentrations in pigs
    after a single intramuscular injection of pST at concentrations of
    0.01 or 1 mg/kg bw showed peak values of 30 ng/ml and 290 ng/ml,
    respectively, after 1 h; the concentrations had returned to baseline
    by 4 and 24 h, respectively (Sillence & Etherton, 1987). The serum
    concentrations of pST in untreated pigs varied from 1.6 to 7 ng/ml
    (Marple & Aberle, 1972; Siers & Trenkle, 1973).

         After repeated daily injections of rpST to pigs, serum
    concentrations did not appear to increase with time, suggesting that
    there it does not accumulate in serum (Chung et al., 1985; Etherton et
    al., 1987; Evock et al., 1988; Campbell et al., 1988).

    2.1.2  Biotransformation

         As rpST is not absorbed intact after oral administration, it has
    no biological activity when given by this route. When doses of 14 mg
    rpST were injected twice weekly into pigs, the blood concentrations of
    somatotropin increased but did not give rise to concentrations in
    muscle tissues that were above physiological levels after 27 h (Schams
    et al., 1989).

    2.1.3  Effects on enzymes and other biochemical processes

         rpST alters the metabolism of tissues such as adipose,
    connective, and bone tissues, liver, skeletal muscle, kidney, thyroid,
    and adrenal gland, and changes the circulating concentrations of
    several nutrients and hormones (Evock et al., 1988; Molon-Noblot et
    al., 1998). Somatotropin directly stimulates cell proliferation
    (Paladini et al., 1984; Isaksson et al., 1985) and also has an
    indirect effect mediated by insulin-like growth factor (IGF-I). The
    synthesis of IGF-I in and secretion from the liver are stimulated
    specifically by somatotropin (Froesch et al., 1985; Mathews et al.,
    1986), and somatotropin may also stimulate local synthesis of IGF-I
    within the target organ itself (Isaksson et al., 1985).

         IGF-I is a 70-amino acid polypeptide hormone of the somatomedin
    family (Klapper et al., 1983). Somatomedins have acute metabolic
    effects similar to but considerably less potent than those of insulin;
    furthermore, IGF-I mediates many of the growth-stimulating effects of
    somatotropin. The serum concentrations of IGF-I are regulated by
    somatotropin, and these change the most dramatically after treatment
    with rpST (Chung et al., 1985; Sillence & Etherton, 1987; Evock et
    al., 1988; Etherton, 1988; Puyt, 1990). The molecular structures of
    porcine and human IGF-I are identical (Tavakkol et al., 1988).

    2.2  Toxicological studies

    2.2.1  Acute toxicity

         The results of studies of the acute toxicity of rpST are
    summarized in Table 1.

    2.2.2  Short-term studies of toxicity

         Rats

         Groups of 20 male and 20 female Sprague-Dawley (Cox SD) albino
    rats were given oral doses of rpST by gavage at concentrations of 0
    (vehicle), 0.04, 0.4, or 4 mg/kg bw per day for 15-22 days. Clinical
    observations and body weights were recorded daily. At the end of the
    study, blood samples were taken and haematological parameters were
    recorded, with measurement of the hormones, triiodothyronine (T3),
    thyroxine (T4), glucagon, and insulin. At necropsy, the organ weights
    were recorded and a thorough histopathological examination was
    performed. The study was not conducted according to appropriate
    standards for study protocol; no statement on observance of GLP was
    provided.

         No clinical signs or toxicological effects were seen during the
    15-22-day test. The death of one male control rat on day 15 was due to
    lung injuries associated with gavage. The body-weight gains of control
    and treated rats were comparable up to day 15. A few variations in
    haematological and clinical chemical parameters were seen, but they
    were spontaneous, often inconsistent by sex, showed a non-linear
    response to rpST dose, and were considered to be unrelated to
    treatment. At necropsy, no gross pathological effect was observed. The
    relative weights of the liver, adrenal, and spleen of male rats and
    the thymus, kidney, brain, and pituitary gland of female rats showed
    some differences from controls that were not related to dose.
    Histopathological examination showed a few microscopic changes suhc as
    mononuclear infiltrates in the portal region of the liver, cortical
    medullary tubular mineralization in the kidneys of male rats, and
    renal cortical tubular nephropathy in controls and rats at the high
    dose. These changes were spontaneous and were considered to be
    unrelated to treatment. The Committee noted that animals in the
    various groups were sacrificed at different times, sometimes by as
    much as seven days. Nevertheless, the values of none of the parameters
    studied were boutside the range of historical controls. No
    treatment-related toxicity was observed in rats at the high dose
    necropsied on day 15. Although the control group was necropsied over
    seven days, it is unlikely that the microscopic lesions seen would
    have changed if all the group had been killed on day 15 (GhiasUddin &
    Wilbur, 1984b).

         In a pilot study, groups of five male and five female
    Sprague-Dawley (Cox SD) albino rats were given oral doses by gavage of
    4 mg/kg bw per day rpST (two lots, one per group) or 4 mg/kg bw per
    day pST for 15 days. Groups of five rats of each sex per group served
    as controls and were given either the vehicle (buffer), 4 mg/kg bw per
    day of egg albumin (protein control), or no treatment. The study was
    conducted in compliance with GLP.

         There were no overt signs of toxicity in any group treated with
    either pST, rpST, or egg albumin during the course of the study. The
    mean body-weight gain on day 15 was similar in each group, and the
    absolute and relative organ weights of rats given pST or rpST were
    comparable and not statistically significantly different from those of
    the various controls. No treatment-related effect was observed on
    routine biochemical parameters at termination. At necropsy, no gross
    pathologican change was noted; there was no histopathological
    examination (GhiasUddin, 1988b).

         Groups of 20 male and 20 female Sprague-Dawley (Crl:CDBR) rats
    were given doses by gavage of 0 (vehicle), 0.44, 4.4, 44, or 130 mg/kg
    bw per day of rpST for 15 days, and groups of 10 males and 10 females
    received daily intramuscular injections of 0.44, 4.4, or 44 mg/kg bw
    per day of rpST; a further 10 males and 10 females given the vehicle
    by intramuscular injection served as controls. Clinical observations
    were made daily, and body weight was recorded before treatment and on
    days 1, 3, 7, 10, and 13 and at the end of the study. Food consumption
    was measured on days 7 and 14. Clinical chemical parameters, including
    determination by radioimmunoassay of the concentrations of circulating
    T3, T4, insulin, and glucagon, and haematological and urinary
    measurements were examined in all animals at the end of the study. All
    rats were necropsied and their organs weighed; the tissues were not
    examined microscopically. Apart from the lack of histopathological
    examination, the study was conducted according to appropriate
    standards for study protocol and conduct.

         There were no adverse clinical signs attributable to treatment.
    One female rat receiving 44 mg/kg bw per day rpST orally died on day
    11 with renal hydropelvis and calculi at necropsy. No statistically
    significant differences were found between the groups treated orally
    and intramuscularly in comparison with the vehicle controls in terms
    of body-weight gain, food consumption, or urinary parameters. No
    treatment-related effects on clinical chemical parameters, organ
    weights, or gross pathological appearance were found in groups treated
    orally when compared with the controls. The mean group values for
    haematological parameters were within the normal reference range for
    this strain of rats but were statistically significantly different     
    ( p < 0.05) from those of their respective vehicle controls, as
    follows: decreased haematocrit in males at 44 and 130 mg/kg bw per day
    orally, decreased haemoglobin in males at 130 mg/kg bw per day orally,
    and increased platelet count in females at 4.4 mg/kg bw per day
    intramuscularly. The clinical chemical changes in rats given rpST

    orally did not alter the blood concentrations of glucagon, insulin,
    T3, T4, total cholesterol, albumin, or aspartate aminotransferase,
    but when rpST was given by intramuscular injection, statistically
    significant ( p < 0.05) changes were seen, as follows: decreased T3
    and increased total cholesterol in males at 4.4 mg/kg bw per day,
    decreased alkaline phosphatase activity, albumin, T3, and T4 in
    males at 44 mg/kg bw per day, and decreased aspartate aminotransferase
    activity in females at 4.4 mg/kg bw per day.

         The mean serum concentrations of rpST in rats 24 h after oral
    treatment were no higher than the mean background levels of vehicle
    control rats treated orally or by intramuscular injection. Some of the
    control animals had concentrations of immunoreactive rpST above the
    detection limit (5 ng/ml, by radioimmunoassay), possibly because of
    non-specific binding of labelled immunoreactive rpST with rat serum
    proteins. Rats given intramuscular injections of 4.4 or 44 mg/kg bw
    per day rpST had mean serum values of 22 and 73 ng/ml of rpST for
    males and 27 and 56 ng/ml for females, respectively. 

         At necropsy, no treatment-related gross pathological changes were
    seen in any of the animals, apart from dark foci in the skeletal
    muscle at the injection site. Rats given rpST by intramuscular
    injection had statistically significantly ( p < 0.05) increased
    weights of the adrenals (absolute and relative) in males at 4.4 and 44
    mg/kg bw per day, of the testes (relative) in males at 44 mg/kg bw per
    day, and of the liver (relative) in females at 44 mg/kg bw per day
    when compared with vehicle controls.

         These results indicate that oral administration of rpST to male
    and female rats at doses of 0.44-130 mg/kg bw per day for 15 days did
    not result in detectable blood concentrations of rpST and did not
    induce any significant physiological responses. In addition, rpST was
    not absorbed from the gastrointestinal tract in a hormonally active or
    immunologically recognizable form and has no significant physiological
    activity when administered orally to rats (GhiasUddin & Bailey, 1988).

         The effects of rpST containing a high level of endotoxin carried
    over from the production technique were investigated in groups of five
    male and five female Sprague-Dawley albino rats given oral doses of 0,
    44, or 130 mg/kg bw per day of rpST or intramuscular injections of 0
    or 44 mg/kg bw per day for 15 days. Apart from the lack of
    histopathological examination, the study was conducted according to
    appropriate standards for study protocol and conduct. No
    treatment-related effects were observed on clinical signs, body-weight
    gain, haematological parameters, creatine kinase, glucagon, glucose,
    insulin, T3, or T4 concentrations, or gross pathological appearance
    (GhiasUddin, 1989).


        Table 1. Acute toxicity of recombinant porcine somatotropin
                                                                                                 

    Species       Route             Sex      Maximum         Effect            Reference
                                             dose
                                                                                                 

    Somagrepor

    Rat           Oral              M, F     5000 mg         None              Fischer (1991a)
    Rabbit        Dermal            M        500 mg/site     None              Fischer (1991b)
    Rabbit        Eye               M        100 mg          Slight            Fischer (1991c)
                                                             irritation

    Reporcin

    Guinea-pig    Dermal            F        12.5 mg/site    None              Bolt (1991a)
    Rabbit        Dermal            F        12.5 mg/site    Mild dermal       Bolt (1991b,
                                                             irritation        1992a,b)

    Rat           Dermal            M,F      1000 mg/kg bw   None              Bolt (1991c)

    Grolene

    Rabbit        Dermal            M,F      2000 mg/kg bw   None              Frank (1989a)
    Rabbit        Dermal            F        500 mg/site     None              Frank (1989b);
                                                                               Sullivan (1985)

    Rabbit        Eye               F        100 mg          None              Franck (1988a)
    Guinea-pig    Dermal            M,F      10 mg/day       None              Gorman & Sullivan
                                                                               (1986);
                                                                               GhiasUddin & Smith
                                                                               (1989);
                                                                               Frank (1988b)

    Guinea-pig    Intradermal       M        0.2 mg/day      Skin              GhiasUddin et 
                                                             sensitization     al. (1984a)

    Guinea-pig    Intratracheal     F        10 mg/ml        Sensitization     Campbell et al.
                                                                               (1989)
                                                                                                 
    

         Four groups of 20 male and 20 female Sprague-Dawley (CD) rats
    were given rpST at concentrations of 0.088, 0.88, 8.8, or 26 mg/kg bw
    per day by gavage for 15 days. Three groups of 20 rats of each sex per
    group served as controls: one was untreated, a second was given the
    vehicle (buffer), and the third received 8.8 mg/kg bw per day of pST
    and served as positive controls. Clinical observations were made
    daily; body weight and food consumption were measured before treatment
    and weekly throughout the study. Haematological, clinical chemical,
    and urinary analyses were performed on 10 rats of each sex from each
    groups at study termination; the measurements included determination
    of the concentrations of circulating T3, T4, insulin, and glucagon.
    All rats were necropsied and their organs were weighed. Only gross
    lesions were examined microscopically. Apart from the limited
    histopathology, the study was conducted according to appropriate
    standards for study protocol and conduct.

         No treatment-related clinical changes were noted, and no
    statistically significant differences from controls were aeen in body
    weight, food consumption, haematological, clinical chemical, or
    urinary parameters, or in absolute or relative organ weights. At
    necropsy, red discolouration of the thymus was seen in some rats of
    each sex, at somewhat higher incidence in treated animals than in
    controls. No concurrent histopathological changes were seen in the
    thymus, and the gross observations were judged to be artefacts induced
    by the exsanguination technique. Increased concentrations of serum T3
    were noted in male rats given 8.8 mg/kg bw per day pST or 26 mg/kg bw
    per day rpST when compared with vehicle controls, but they were
    comparable to those of untreated controls. The plasma glucagon
    concentrations were statistically significantly decreased in males
    given 8.8 or 26 mg/kg bw per day rpST or 8.8 mg/kg bw per day pST when
    compared with vehicle controls (Sullivan & Atkinson, 1986).

         In order to corroborate the increased serum concentrations of T3
    and the decreased glucagon concentrations, two additional 15-day
    studies in rats were carried out in two independent laboratories. The
    study design was similar to that of Sullivan & Atkinson, except that
    organs were not weighed; particular attention was paid to the
    collection, handling, and analysis of blood samples. The studies were
    conducted in compliance with GLP.

         Neither study reproduced the effects on circulating hormone
    concentrations after daily oral administration of rpST or pST, and
    there were no treatment-related effects on clinical appearance,
    body-weight gain, blood concentrations of glucagon, insulin, T3, T4,
    or glucose, or gross pathological appearance (Sullivan, 1987;
    GhiasUddin & Waterhouse, 1987).

         Groups of 10 male and 10 female Charles River CDR rats were given
    rpST by gavage at 0 (vehicle), 0.25, 2.5, or 25 mg/kg bw per day for
    21 days. A fifth group of 10 male and 10 female rats received rpST by
    subcutaneous injection at a dose of 2.5 mg/kg bw, also for 21 days.
    Clinical observations were made daily, and body-weight gain and food
    consumption were recorded weekly. At the end of the study, blood
    samples were taken and haematological and clinical chemical parameters
    were measured. At necropsy, organ weights were recorded and a thorough
    histopathological examination was performed. The study was conducted
    according to appropriate standards for study protocol and conduct.

         Apart from the death of two female rats given 25 mg/kg bw per day
    of rpST orally, which were due to accidents during gavage, no clinical
    signs of toxicity were observed. There were no treatment-related
    differences between orally-treated animals and controls in terms of
    body-weight gain, food consumption, haematological or clinical
    chemical parameters, gross or histopathological appearance, or
    absolute or relative organ weights. The group treated subcutaneously
    with 2.5 mg/kg bw per day of rpST had increased body-weight gain,
    which was not significant for males and significant ( p < 0.05) for
    females. No other effects were observed in the group treated
    subcutaneously (Fischer, 1992).

         Dogs

         Thirty-two beagle dogs, 54-69 weeks old and weighing 6.9-16 kg,
    were randomized to groups of four males and four females and given
    subcutaneous injections of pST (native or recombinant not specified)
    at doses of 0 (vehicle), 0.014, 0.05, or 0.55 mg/kg bw per day for 14
    weeks. Clinical observations were made daily, food consumption was
    determined four times per week, and body weights were recorded weekly.
    Haematological, and clinical chemical parameters were determined after
    3, 7, 11, and 14 weeks of treatment. Necropsy, organ weighing, and
    histopathology were performed at the end of the study. 

         During the study, all treated dogs developed increased skin
    thickness, especially on the head, which was histologically correlated
    to thickening of dermal collagen. All dogs survived the study, and
    those at the intermediate and high doses had a dose-related decrease
    in body-weight gain. Persistent, statistically significant 
    ( p < 0.05) normochromic normocytic anaemia developed in dogs at the 
    high dose after three weeks of treatment and was seen in those at the 
    low dose after seven weeks. From week 3 onwards, a statistically
    significant ( p < 0.05) decrease in serum urea nitrogen and creatinine
    was seen in dogs at the high dose and increases in serum alkaline
    phosphatase activity, calcium, phosphorus, potassium, cholesterol, and
    triglyceride concentrations were found in dogs at the intermediate and
    high doses. The serum concentrations of T3, T4, and cortisol were
    unaffected by treatment. Dogs at the high dose showed polyuria
    associated with decreased specific gravity of the urine.

         At the end of the study, the absolute and relative weights of the
    liver and kidneys of animals of each sex and of the adrenals in males
    were statistically significantly ( p < 0.05) increased. Dose-related
    histopathological changes were seen in all groups, comprising
    cytoplasmic rarefaction of pancreatic islet cells, renal mesangial
    thickening, lateral widening of the cartilage-bone junction of the
    ribs and focal osteoblast proliferation, physis thickening of the
    bones, erythroid depletion of the bone marrow, extramedullary
    haematopoiesis of the spleen, rarefaction of hepatocytes (at the
    intermediate and high doses), and mucous cell hyperplasia of the
    glandular stomach (at the intermediate and high doses) (Prahalada et
    al., 1998).

         Pigs

         A number of studies in pigs of the effects of pST or rpST on
    growth and other biological parameters after parenteral administration
    were reported which were nor designed to comply with accepted
    standards for the protocol and conduct of studies of toxicity.

         Groups of 12 Yorkshire barrows weighing 32 kg received
    intramuscular injections of 0 or 0.022 mg/kg bw per day of pST for 30
    days. The pigs were individually penned and fed a corn-soyabean-based
    diet formulated to contain 16% protein  ad libitum. One animal treated
    with pST was withdrawn during the study because it developed
    proliferative ileitis. At the end of the study, the treated pigs
    showed increased ( p < 0.05) body-weight gain and feed efficiency;
    the serum concentrations of glucose, triglycerides, urea nitrogen,
    pST, and IGF-I were comparable to those of controls. The serum insulin
    concentration of pST-treated pigs was increased during the study but
    not at termination. No pST antibodies were detected in plasma. The
    absolute weights of the liver, kidney, and heart of treated pigs was
    increased ( p < 0.05), while the weight of the pancreas was
    comparable to that of controls. No histopathological changes were
    observed in lung, thyroid, adrenal, liver, kidney, spleen, myocardium,
    skeletal muscle, or intestine. The weight of the pituitary gland was
    not affected by pST treatment, but the concentration of pST per mg
    pituitary gland was reduced ( p < 0.001) more than 40%. No effect on
    carcass adipose tissue mass was seen after treatment, but the carcass
    muscle mass was increased ( p < 0.01) in comparison with controls
    (Chung et al., 1985).

         In a subsequent study, the results of Chung et al. (1985) were
    confirmed in pigs that received pST by intramuscular injection at
    doses of 0, 0.01, 0.03, or 0.07 mg/kg bw per day for 35 days. The
    dose-related effect of pST on increasing feed efficiency and carcass
    muscle mass and decreasing carcass lipid mass indicate that metabolic
    effects and stimulation of growth can be expected at doses below 0.01
    mg/kg bw per day and do not have an upper limit at 0.07 mg/kg bw per
    day (Etherton et al., 1987).

         Groups of 12 Yorkshire-Duroc barrows weighing 27 kg received
    daily intramuscular injections of pST at doses of 0, 0.035, or 0.07
    mg/kg bw or rpST at 0.035, 0.07, or 0.14 mg/kg bw for 77 days. The
    growth rate was increased and feed efficiency was improved similarly
    by pST and rpST. The improved feed efficiency was associated with a
    decrease in feed intake. Both pST and rpST increased carcass muscle
    mass, while rpST was less effective in decreasing carcass lipid mass.
    All of the other parameters measured, including serum concentrations
    of glucose, insulin, blood urea nitrogen, pST, rpST, and IGF-I,
    indicated that rpST mimics the biological effects of pST, including
    binding to pig liver membranes and induction of IGF-I production
    (Evock et al., 1988).

         As use of pST in pigs may affect their mobility, investigations
    have been conducted on leg soundness focusing on the major part of the
    bones, the growth centres, and the joints. Daily treatment with rpST
    progressively affected the physical mobility of pigs (initial body
    weight, 27 kg) over a period of 11 weeks, and doses of 0.07 and 0.14
    mg/kg bw, but not 0.035 mg/kg bw, caused an increased ( p < 0.05)
    incidence of osteochondrosis in the growth centres of the femur and
    tibia characterized by focal deep zones of hypertrophied chondrocytes
    protruding into the metaphysis. No concurrent differences in the
    calcium or phosphorus concentrations of bones or serum were observed
    (Evock et al., 1988).

         Pigs weighing 40 kg and treated daily with pST at 0.1 mg/kg bw
    for eight weeks had an increased ( p < 0.05) incidence and increased
    severity of osteochondrotic lesions of the articular-epiphyseal
    complex of the humerus and ulna when compared with controls (Carlson
    et al., 1988).

         The weight and length of the humerus and ulna and the cartilage
    thickness of their distal joints were increased ( p < 0.05) in pigs
    treated daily with 4 mg pST for six weeks when compared with controls
    (Joergensen & Tang Sorensen, 1994).

         When osteochondrotic lesions were scored on a three-point scale,
    the forelimbs of control pigs had an average score of 1.06 while those
    of pigs treated with 4 mg rpST per day from a weight of 55 to 109 kg
    had a score of 1.43; the differences in soundness scores on a
    nine-point scale approached significance (6.5 versus 5.3;  p < 0.10)
    (Skaggs et al., 1989a). The reported prevalence and severity of
    osteochondrotic lesions were associated with increased body-weight
    gain (Skaggs et al., 1989a) and with increased somatotropin serum
    concentrations in pigs selected for rapid growth (Arbona et al.,
    1988).

         The effects of rpST on quantitative and qualitative carcass
    traits were investigated in genetically selected normal and
    stress-susceptible pigstreated with 4 mg rpST per day from 55 to 109
    kg body weight. The meat of genetically selected stress-susceptible

    pigs was improved with regard to muscle pH and colour by rpST
    treatment (Skaggs et al., 1989b). In another study, treatment with pST
    at 2 or 4 mg/day for 75 days improved the carcass composition without
    increasing the incidence of pale, soft, exudative meat (Ender et al.,
    1989).

         The immunotoxicity of rpST was studied in groups of growing pigs
    which received intramuscular injections of doses of 5, 15, or 25
    mg/head for 57 days. One group received the vehicle and served as
    controls. No consistent, significant affect of rpST treatment was
    observed on the gross or histopathological appearance of the organs of
    the immune system, total and differential leukocyte counts, antibody
    titres to  Actinobacillus pleuropneumonia isolates of
     B. bronchiseptica, and  P. multocida from nasal swabs, the
    lymphocytic blastogenic response to mitogens, or the neutrophil
    functions of chemotaxis, ingestion, reduction of cytochrome c, and
    antibody-dependent cell-mediated cytotoxicity. Significantly effects
    of rpST-treatment included decreased haemoglobin and packed cell
    volume, increased random neutrophil migration, and a temporary
    decrease in the IgG antibody response to tetanus toxoid. There was no
    observed effect on the overall clinical health of the treated pigs
    (Goff et al., 1991).

    2.2.3  Reproductive toxicity

         Information was available only on pigs. A number of studies have
    been carried out in pigs to investigate the effects of pST on
    reproduction, including maternal sexual maturation, fetal development,
    and post-natal performance. Parenteral administration was used in all
    of the studies.

         Cultured ovarian granulosa cells derived from prepubertal gilts
    treated with pST at a dose of 0.07 mg/kg bw for 25 days produced more
    progesterone in the presence of luteinizing hormone or
    follicle-stimulating hormone than cells from control gilts (Bryan et
    al., 1988). In another study, however, a reduced response of granulosa
    cells to gonadotropin was found  in vitro (Bryan et al., 1989).

         In young boars, treatment with rpST at a dose of 3.5 or 7 mg/day
    from 70 to 118 kg body weight did not affect the weights of the
    reproductive organs and glands or serum testosterone concentrations
    (Hagen et al., 1989)

         The age at puberty, the length of estrus, the length of the
    estrus cycle, and the ovulation rates at second oestrus of gilts
    treated with pST at a dose of 6 mg/day from 50 to 110 kg body weight
    were similar to those of controls (Terlouw et al., 1991). Similar
    results were found in prepubertal gilts treated with 5 mg/day for 30
    days (Bryan et al., 1990).

         In gilts treated with rpST at a dose of 5 mg/day on days 30-43
    of gestation, fetal and implantation length were not affected, but
    fetal and placental weights and maternal serum IGF-I concentrations
    were increased ( p < 0.05) when compared with controls (Sterle et
    al., 1995). 

         Sows were given rpST by injection at a dose of 6 mg/day from day
    108 of gestation to day 28 of lactation. The litter size was
    standardized at 8-10 piglets per litter on day 3 of lactation. The
    milk yield and average piglet weaning weights were not affected by
    treatment. In a second study, similar results were found in sows
    receiving 70 mg rpST on days 3, 10, 17, and 24 of lactation (Cromwell
    et al., 1992). Daily injection of 10 mg/day rpST of sows with their
    first litter on days 8 and 39 of lactation did not change the milk
    yield or composition with respect to fat, protein, and lactose content
    in comparison with controls (Toner et al., 1996). In another study, an
    increased fat content was found in colostrum and in milk at day 13 but
    not at day 20, and increased milk production was found by three weeks
    in sows treated with 5.3 mg/day pST during the last 13 days of
    gestation and the first 21 days of lactation.

         In sows and gilts treated with pST at 10 mg/day during the last
    21 days of gestation, no effects were found on birth weight, the
    number born alive, or 21-day survival; however, one gilt and three
    sows out of 20 treated pigs died before or at delivery (Kveragas et
    al., 1986). Sows treated with 5 or 15 mg/day rpST during the last 14
    days of gestation had litters with increasing birth weight ( p <
    0.10), but this result was not confirmed in a subsequent study which
    showed no effect on birth weight, weaning weight, or survival at day
    21 among the offspring of sows treated with 4 or 8 mg/day pST from day
    94 of gestation through weaning (Baile et al., 1989).

    2.3  Observations in humans

         During the 1950s several clinical trials were conducted of the
    injection of pituitary preparations derived from farm animals,
    including pigs, into humans for treatment of dwarfism. Although some
    of the initial studies were thought to show an effect, the porcine
    pituitary preparations did not stimulate growth in humans (Raben,
    1959; Kaplan, 1965) or in hypophysectomized monkeys (Knobil & Greep,
    1959). Serum triglycerides were not affected in humans (Raben, 1959).
    Mills et al. (1976) also failed to detect any metabolic activity for
    the retention of nitrogen, phosphorus, potassium, sodium, and
    chloride; they found no increase in plasma free fatty acids, no
    decrease in plasma alpha-amino nitrogen, no impaired glucose 
    tolerance, and no hyperinsulinaemia in growth hormone-deficient 
    children after injection of either native pST or serum 
    plasmin-digested pST. It was concluded that somato-tropins were 
    species-limited with somatotropins from lower species having no 
    activity in humans. The biological basis for this species specificity 
    was discovered years later when it was determined that the binding of 
    pST to the human somatotropin receptor is several orders of magnitude 
    lower than that of human somatotropin (Carr & Friesen, 1976).

    2.4  Short-term toxicity of insulin-like growth factor

         IGF-I, given as recombinant human somatomedin-C, was administered
    by gavage at doses of 0.1, 0.25, or 0.5 mg/kg bw per day to three
    groups of 25 male and 25 female hypophysectomized Sprague-Dawley
    (Crl:CDBR) rats for 15 days. Three control groups, each consisting of
    25 male and 25 female rats, were given the vehicle (buffer) orally by
    gavage, a single daily intramuscular injection of IGF-I at 0.5 mg/kg
    bw, or a single daily intramuscular injection of the vehicle. Clinical
    observations, body weights, food consumption, haematological, urinary,
    and clinical chemical parameters (including adrenocorticotropic
    hormone, glucagon, cortisol, insulin, T3, and T4), gross
    pathological appearance, and organ weights were assessed. Tissues were
    not examined microscopically. Apart from the limited histopathological
    examination, the study was conducted according to appropriate
    standards for study protocol and conduct.

         The treatment with IGF-I did not cause any clinical signs of
    toxicity during the study. The mean values for food consumption, body
    weight (days 1-13), and body-weight gain of treated male and female
    rats were comparable to those of the controls, and no
    treatment-related abnormalities were seen at necropsy. The only
    difference from controls in absolute and relative organ weights was a
    statistically significant ( p < 0.05) increase in relative kidney
    weight and an inverse dose-related decrease in terminal body weight of
    female rats given 0.25 or 0.5 mg/kg bw per day. Haematological,
    urinary, and clinical chemical parameters were not affected by
    treatment, except for a statistically significant ( p < 0.05) decrease
    in serum glucose in female rats, which was also observed in control
    females receiving vehicle by intramuscular injection. The authors
    considered the observed decrease in serum glucose in female rats to be
    of doubtful biological significance as the changes were small and not
    related to dose. The serum concentrations of IGF-I were below the
    limit of detection (7 ng/ml) 2.5-3.5 h after the last treatment in all
    animals treated orally. IGF-I was found by a validated
    radioimmunoassay in the serum of rats given IGF-I by intramuscular
    injection at mean concentrations of 72 and 90 ng/ml in male and female
    rats, respectively. Intramuscular injection increased the platelet
    counts in females, decreased the serum glucose concentration in
    females, decreased alanine aminotransferase activity in males,
    decreased the total cholesterol concentration in females, decreased
    the albumin concentration in males, and decreased the relative weight
    of the liver in males. Two female vehicle controls died on days 5 and
    9 of the study from unidentified causes. Thus, no toxicological or
    physiological effects were seen in hypophysectomized rats treated
    orally for two weeks with IGF-I at doses up to 0.5 mg/kg bw per day
    (Howard & Bailey, 1989; Edwards et al., 1989). 

         Similar results were reported from two other studies of
    hypophysectomized rats given IGF-I orally at doses up to 1 or 2 mg/kg
    bw per day for two weeks (Juskevich & Guyer, 1990).

         The half-lives of 125I-labelled IGF-I in fasted adult rats were 8
    min in the stomach, 2 min in ligated segments of the duodenum, 2 min
    in the ileum, and 38 min in the colon. Results obtained  in vitro
    were comparable except that IGF-I was degraded more rapidly in the
    colon  in vivo (Xian et al., 1995).

    3.  COMMENTS

         The Committee considered the results of studies on the acute and
    short-term toxicity and reproductive toxicity of pST and rpST and the
    results of studies on IGF-I, the production of which is stimulated by
    somatotropin. All of the pivotal studies of toxicity were performed
    according to appropriate standards for study protocol and conduct.
    Most of the short-term studies focused on effects on biological
    parameters such as body-weight gain, ahematology, and clinical
    chemistry after oral or parenteral administration of rpST, and only a
    few included comprehensive histopathological examination.

         Somatotropin and IGF-I are found in all mammalian species. The
    structural homology between porcine and human somatotropin is
    approximately 66%. The differences in amino acid sequences result in
    the 'species specificity' of somatotropins. Pituitary-derived pST is
    biologically inactive when injected into hypphysectomized rhesus
    monkeys and in humans who have received pST or plasmin-digested pST by
    injection. In addition, it has been shown that pST does not bind to
    human somatotropin receptors in liver  in vivo. Rats displayed a
    physiological response to parenterally administered pST and rpST,
    although the hormones are about 250 times less potent in this species
    than in pigs. The physiological effects of rpST were indistinguishable
    from those of native pST in pigs or hypophysectomized rats after
    parenteral administration. pST and rpST showed similar inhibition of
    binding of 125I-labelled pST to liver microsomal membrane fractions
    from pigs or rabbits  in vitro.

         Peak serum concentrations of pST in rats occurred 6 h after an
    intramuscular injection of 125I-labelled rpST, while pST was no longer
    measurable 60 h after treatment. The biological serum half-life was
    not established in rats. The half-lives of 125I-pST and 125I-rpST in
    pigs are short and were determined to be 4 min for the fast phase and
    up to 49 min for the slow phase. Biodegradation appears to be rapid,
    and parenterally administered rpST at the doses used for growth
    promotion in pigs did not lead to concentrations of pST in blood or
    muscle that were greater than the physiological levels 27 h after
    treatment.

         A study in rats given rpST as single doses of up to 5 g/kg bw
    showed no biological or toxicological effect. No adverse biological
    effects were observed in a study in which rats were given pST or rpST
    orally at a dose of 4 mg/kg bw per day for 15 days, and in two 15-day
    studies in which rats were given rpST at doses up to 130 mg/kg bw per
    day, no adverse effects were seen and no pST could be found in serum.

    In a comprehensive study in rats given rpST at doses up to 26 mg/kg bw
    per day or pST at 8.8 mg/kg bw per day, no clinical signs of toxicity
    or treatment-related changes in body-weight gain, haematological,
    clinical chemical, or urinary parameters, organ weights, or gross
    pathological appearance were observed. A statistically significant
    decrease in the serum concentration of glucagon was observed in male
    rats at 8.8 and 26 mg of rpST and 8.8 mg of pST per kg bw per day;
    however, the observed effect on serum glucagon concentration was not
    reproduced in two additional studies of identical design which were
    conducted in two independent laboratories. In a further study, oral
    administration of rpST to rats at 25 mg/kg bw per day for 21 days did
    not cause treatment-related histopathological changes. These studies
    demonstrated that pST and rpST have no biological activity when
    administered orally.

         When rpST was given intramuscularly to rats for 15 days,
    decreased concentrations of the thyroid hormones triiodothyronine and
    thyroxine, decreased activities of serum alkaline phosphatase and
    aspartate aminotransferase, decreased albumin concentrations, and
    increased serum cholesterol concentrations, platelet counts, and
    weights of the liver, testis, and adrenal were observed at doses of
    4.4 mg/kg bw per day and above.

         In several studies, pigs weighing 27-40 kg were treated
    parenterally with pST or rpST at doses of 0.01-0.07 mg/kg bw per day
    for up to 77 days. The observed effects included increased body-weight
    gain, feed efficiency, serum glucose, triglycerides, blood urea
    nitrogen, and IGF-I concentrations, and increased weights of the
    liver, kidneys, and heart. These effects were considered to be due to
    specific binding of pST and rpST to pST receptors. Doses of 0.035 mg
    of pST or rpST per kg bw or above affected the physical mobility of
    the pigs by causing lesions of the bone and cartilage of the major leg
    joints. Since pST and rpST do not bind to the human somatotropin
    receptor, the Committee considered that the effects seen in pigs are
    unlikely to occur in humans. No effect on key immune functional
    parameters was observed in pigs receiving daily intramuscular
    injections of rpST at doses of up to 25 mg/animal for 57 days.

         No information was available on the reproductive toxicity of pST
    or rpST in laboratory animals. Reproductive effects in pigs given
    intramuscular injections of approximately 5 mg of pST or rpST per
    animal per day were investigated in a number of studies. No effects
    were observed on the age at onset of puberty, length of estrus or
    estrus cycle, or ovulation rate in nulliparous sows, while treatment
    of pregnant nulliparous sows increased placental and fetal weights.
    The lactation performance of sows and the composition of their milk
    were not affected. Treatment of sows late in gestation and during
    lactation had no effect on the birth weight of their offspring, the
    number of live births, or survival up to 21 days.

         No information was available on the genotoxic potential of rpST,
    but the Committee noted that the structurally related compound
    recombinant bovine somatotropin did not show evidence of genotoxicity
    in two assays (Annex 1, reference  135).

         Many of the physiological effects of somatotropin are mediated by
    IGF-I. The chemical structures of human, porcine, and bovine IGF-I are
    idential. The bioactivity of IGF-I residues in tissues and milk was
    considered at the fortieth meeting in relation to use of bovine
    somatotropin (Annex 1, reference  104). At that time, the Committee
    concluded that, although the liver is the major site of IGF-I
    synthesis, it is also present in human milk, saliva, and pancreatic
    secreations. The Committee further concluded that IGF-I is not
    biologically active when administered orally to hypophysectomized
    rats, as dietary IGF-I is almost completely degraded by digestive
    enzymes and is not expected to contribute significantly to the high
    endogenous concentration of IGF-I in the intestine.

    4.  EVALUATION

         Using data considered at the fiftieth meeting, when recombinant
    bovine somatotropins were last evaluated (Annex 1, reference  134),
    the Committee concluded at its present meeting that when rpST is used
    in pigs, the excess levels of IGF-I residues in edible tissues are
    orders of magnitude lower than the amount produced endogenously in
    humans and are therefore extremely unlikely to represent any health
    risk for consumers.

         The Committee noted that recombinant proteins may cause allergy;
    however, because there was no evidence that pork meat, which contains
    pST, is allergenic in humans and because rpSTs are antigenically
    similar to native pST, residues of rpST in food are not likely to
    cause an allergic response in humans after consumption.

         In reaching a conclusion on the safety of rpST, the Committee
    noted the following:

    *    the lack of biological activity of rpST in rats after oral
         administration;

    *    the lack of biological activity of rpST in humans, as evidenced
         by the substantial difference in the amino acid sequence of
         somatotropin from pigs and humans, the absence of binding of rpST
         to human somatotropin receptors, and the lack of effect in humans
         injected with either pST or serum plasmin-digested pST; and

    *    the lack of biological activity of ingested IGF-I.

         From the above, the Committee concluded that rpST can be used in
    pigs without any appreciable health risk for consumers from the
    administered rpST or from IGF-I residues in rpST-treated pigs. It
    established an ADI 'not specified'1 for rpST, which applies to the
    three products that were evaluated at the present meeting.

    5.  ACKNOWLEDGEMENTS

         Dr K. Sejrsen and Dr T. Tang-Sorensen, Danish Institute of Animal
    Science, Denmark, are acknowledged for their assistance with the
    preparation of the first draft of this monograph.

    6.  REFERENCES

    Arbona, J.R., Marple, D.M., Russell, R.W., Rahe, C.H., Mulvaney, D.R.
    & Sartin, J.L. (1988) Secretory patterns and metabolic clearance rate
    of porcine somatotropin in swine selected for growth.  J. Anim. Sci.,
    66, 3068-3072.

    Baile, C.A., Azain, M.J., Buonomo, F.C. & Kasser, T.R. (1989) Effect
    of somatotropin treatment in sows during late gestation on birth
    weight and performance of pigs.  J. Anim. Sci., 67 (Suppl.1), 214
    (Abstract No.528).

    Biroc, S.E. (1992) Comparison of recombinant porcine somatotropin
    (rPST, CL 300,548) with A6T:S11R:C183E:C191E-PST (CL 326,061) using
    hypophysectomized rat weight gain test. Unpublished report no. FD
    40-9.00 from American Cyanamide Company. Submitted to WHO by Cyanamide
    Australia Pty Ltd, Baulkham Hills, New South Wales, Australia.

    Bolt, A.G. (1991a) Skin sensitization potential in the guinea pig of
    porcine somatotropin CSL batch 5#. Unpublished report No. T1469E from
    Pharmatox, New South Wales, Australia. Submitted to WHO by Pharmaction
    Pty Ltd, Laverton North, Victoria, Australia.

    Bolt, A.G. (1991b) Acute dermal irritation in the rabbit of porcine
    somatotropin CSL batch 5#. Unpublished report No. T1469D from
    Pharmatox, New South Wales, Australia. Submitted to WHO by Pharmaction
    Pty Ltd, Laverton North, Victoria, Australia.

                       
    1    ADI 'not specified' is allocated when the available data on the
         toxicity and intake of a veterinary drug indicate a large margin
         of safety from consumption of residues in food when the drug is
         used according to good practice in the use of veterinary drugs.
         For that reason and for the reasons stated in the evaluation of
         the drug, the Committee concluded that use of the veterinary drug
         does not represent a hazard for human health and that there is no
         need to specify a numerical ADI.

    Bolt, A.G. (1991c) Acute dermal toxicity test of porcine somatotropin
    CSL batch 5# in the rat. Unpublished report No. T1469C from Pharmatox,
    New South Wales, Australia. Submitted to WHO by Pharmaction Pty Ltd,
    Laverton North, Victoria, Australia.

    Bolt, A.G. (1992a) Acute dermal irritation in the rabbit of porcine
    somatotropin in carbonate buffer. Unpublished report No. T1488B2 from
    Pharmatox, New South Wales, Australia. Submitted to WHO by Pharmaction
    Pty Ltd, Laverton North, Victoria, Australia.
 
    Bolt, A.G. (1992b) Acute dermal irritation in the rabbit of porcine
    somatotropin in ethanolamine buffer. Unpublished report No. T1488B1
    from Pharmatox, New South Wales, Australia. Submitted to WHO by
    Pharmaction Pty Ltd, Laverton North, Victoria, Australia.

    Bryan, K.A., Clark, A.M., Hagen, D.R. & Hammond, J.M. (1988) Effect of
    doses of porcine somatotropin (pST) on growth, carcass traits and
    granulosa cell function of gilts.  J. Anim. Sci., 66 (Suppl. 1),
    379 (Abstract No. 384). 

    Bryan, K.A., Hammond, J.M., Canning, S., Mondschein, J., Carbaugh,
    D.E., Clark, A.M. & Hagen, D.R. (1989) Reproductive and growth
    responses of gilts to exogenous porcine pituitary somatotropin.
     J. Anim. Sci., 67, 196-205.

    Bryan, K.A., Clark, A.M. & Hagen, D.R. (1990) Effects of treatment
    with and subsequent withdrawal of exogenous porcine somatotropin on
    growth and reproductive characteristics of gilts.  J. Anim. Sci.,
    68, 2357-2361. 

    Campbell, R.G., Steele, N.C., Caperna, T.J., McMurtry J.P., Solomon,
    M.B. & Mitchell, A.D. (1988) Interrelationships between energy intake
    and endogenous porcine somatotropin administration on the performance,
    body composition and protein and energy metabolism of growing pigs
    weighing 25 to 55 kilograms live weight.  J. Anim. Sci., 66,
    1643-1655.

    Campbell, D.G., Buehler E.V., Kreuzmann J.J. & Lewis, D.K. (1989)
    Intratracheal study of P-3895 in guinea pigs. Unpublished report No.
    PLR 1020 from Pitman-Moore, Inc. Submitted to WHO by Pharmaction Pty
    Ltd, Laverton North, Victoria, Australia.

    Carlson, C.S., Wood, C.M. & Kornegay, E.T. (1988) Effect of porcine
    somatotropin on the severity of lesions of osteochondrosis in swine.
    Proc. IPVS, p. 235.

    Carr, D. & Friesen, H.C. (1976) Growth hormone and insulin binding to
    human liver.  J. Clin. Endocrinol. Metab., 42, 484-483.

    Chung, C.S. & Etherton, T.D. (1986) Characterisation of porcine
    somatotropin (pST) binding to porcine liver microsomes: Chronic
    administration of pST induces pST binding.  Endocrinology, 119,
    780-786.

    Chung, C.S., Etherton, T.D. & Wiggins, J.P. (1985) Stimulation of
    swine growth by porcine somatotropin.  J. Anim. Sci., 60, 118-130.

    Cromwell, G.L., Stahly, T.S., Edgerton, L.A., Monegue, H.J., Burnell,
    T.W., Schenck, B.C. & Schrick, B.R. (1992) Recombinant porcine
    somatotropin for sows during late gestation and throughout lactation.
     J. Anim. Sci., 70, 1404-1416.

    Cyanamide (1992) Part 1--Product identity and summaries. Unpublished
    report from Cyanamide. Submitted to WHO by Cyanamide Australia Pty
    Ltd, Baulkham Hills, New South Wales, Australia.

    Eager, K.B. (1992) A comparison of recombinant porcine somatotropin
    (PST) analog, A6T:S11R:C183E:C191E-PST (CL 326,061), to recombinant
    PST (CL 300,548) on the growth performance and carcass composition of
    finishing pigs. Unpublished report no. FD 40-6.00 from American
    Cyanamide Company. Submitted to WHO by Cyanamide Australia Pty Ltd,
    Baulkham Hills, New South Wales, Australia.

    Edwards, C.K., Ferrin, M.A. & Tully, D.A. (1989) Validation of the
    immunoradiometric assay (IRMA) for determination of recombinant human
    somatomedin-C (rHuSmC) levels in serum from normal and
    hypophysectomized rats. Unpublished report No. MR-4554 from
    Pitman-Moore, Inc. Submitted to WHO by Pharmaction Pty Ltd, Laverton
    North, Victoria, Australia.

    Ender, K., Lieberenz, M., Poppe, S., Hackl, W., Pflughaupt, G. &
    Meisinger, D. (1989) Effect of porcine somatotropin (pST) treatment on
    growing-finishing pigs: Carcass characteristics.  J. Anim. Sci., 67
    (Suppl. 1), 212 (Abstract No. 523).

    Etherton, T.D. (1988) The mechanisms by which porcine growth hormone
    improves pig growth performance. In: Heap, R.B., Prosser G.G. &
    Lamming, G.E., eds,  Biotechnology in Growth Regulation, London,
    Butterworths, pp. 97-105.

    Etherton, T.D., Wiggins, J.P., Evock, C.M., Chung, C.S., Rebhun, J.F.,
    Walton, P.E. & Steele, N.C. (1987) Stimulation of pig growth
    performance by porcine somatotropin: Determination of the
    dose-response relationship.  J. Anim. Sci., 64, 433-443.

    Evock, C.M., Etherton, T.D., Chung, C.S. & Ivy, R.E. (1988) Pituitary
    porcine somatotropin (pST) and a recombinant pST analog stimulate pig
    growth performance in a similar manner.  J. Anim. Sci., 66,
    1928-1941.

    Fischer, J.E. (1991a) Oral LD-50 study in the albino rat with
    recombinant porcine somatotropin. Unpublished report No. A91-11 from
    American Cyanamide Company. Submitted to WHO by Cyanamide Australia
    Pty Ltd, Baulkham Hills, New South Wales, Australia.

    Fischer, J.E. (1991b) Skin irritation study in albino rabbits with
    recombinant porcine somatotropin. Unpublished report No. A91-6 from
    American Cyanamide Company. Submitted to WHO by Cyanamide Australia
    Pty Ltd, Baulkham Hills, New South Wales, Australia.

    Fischer, J.E. (1991c) Eye irritation study in albino rabbits with
    recombinant porcine somatotropin. Unpublished report No. A91-5 from
    American Cyanamide Company. Submitted to WHO by Cyanamide Australia
    Pty Ltd, Baulkham Hills, New South Wales, Australia.

    Fischer, J.E. (1992) Recombinant porcine somatotropin: A 21-day rat
    oral/subcutaneous toxicity study. Unpublished report No. AX92-1 from
    American Cyanamide Company. Submitted to WHO by Cyanamide Australia
    Pty. Ltd., 5 Gibbon Road, Baulkham Hills NSW 2153, Australia.

    Frank, P. (1988a) Eye irritation potential of P-3895 (porcine
    somatotropin) in rabbits. Unpublished report No. PLR 88RAB005 from
    Pitman-Moore. Inc. Submitted to WHO by Pharmaction Pty Ltd, Laverton
    North, Victoria, Australia.

    Frank, P. (1988b) Topical dermal sensitisation test of P.-3895
    (porcine somatotropin) in guinea pigs. Unpublished report No. PLR
    88PG002 from Pitman-Moore, Inc. Submitted to WHO by Pharmaction Pty
    Ltd, Laverton North, Victoria, Australia.

    Frank, P. (1989a) Acute dermal toxicity of P-3895 (porcine
    somatotropin) in rabbits. Unpublished report No. PLR 88RAB006 from
    Pitman-Moore. Inc. Submitted to WHO by Pharmaction Pty Ltd, Laverton
    North, Victoria, Australia.

    Frank, P. (1989b) Primary dermal irritation test of P-3895 (porcine
    somatotropin) in rabbits. Unpublished report No. PLR 88RAB007 from
    Pitman-Moore. Inc. Submitted to WHO by Pharmaction Pty Ltd, Laverton
    North, Victoria, Australia.

    Froesch, E.R., Schmid, C., Schwander, J. & Zapf, J. (1985) Actions of
    insulin-like growth factors.  Ann. Rev. Physiol., 47, 443-467.

    GhiasUddin, S.M. (1988a) Biological half-life of the recombinant and
    pituitary-derived porcine somatotropin in swine. Unpublished report
    No. PLR 1005 from Pitman-Moore, Inc. Submitted to WHO by Pharmaction
    Pty Ltd, Laverton North, Victoria, Australia.

    GhiasUddin, S.M. (1988b) Pilot study--Subacute oral toxicity of
    recombinant and natural porcine somatotropin (rpST, P-3232; rpST,
    P-3230) in rats. Unpublished report No. PLR 658 from Pitman-Moore,
    Inc. Submitted to WHO by Pharmaction Pty Ltd, Laverton North,
    Victoria, Australia. 

    GhiasUddin, S.M. (1989) A 15-day study of recombinant porcine
    somatotropin administered to rats orally or by intramuscular
    injection: Effects on glucose, CPK and circulating hormone levels.
    Unpublished report No. PLR 87RAT002 from Pitman-Moore, Inc. Submitted
    to WHO by Pharmaction Pty Ltd, Laverton North, Victoria, Australia.

    GhiasUddin, S.M. & Bailey, D.E. (1988) A 15-day oral dosing and
    intramuscular injection study in rats with porcine somatotropin (pST,
    P-3895). Unpublished report No. PLR 87RAT005 from Pitman-Moore, Inc.
    Submitted to WHO by Pharmaction Pty Ltd, Laverton North, Victoria,
    Australia.

    GhisaUddin, S.M. & Smith, S. (1989) Screen test: Topical dermal
    sensitisation potential of pituitary derived natural and recombinant
    porcine somatotropins in guinea pigs. Unpublished report No. PLR-1016
    from Pitman-Moore, Inc. Submitted to WHO by Pharmaction Pty Ltd,
    Laverton North, Victoria, Australia.

    GhiasUddin, S.M. & Waterhouse, G.A.W. (1987) A 15-day oral dosing
    study in rats with porcine somatotropin (pST, P-3895). Unpublished
    report No. PLR 984 from Pitman-Moore, Inc. Submitted to WHO by
    Pharmaction Pty Ltd, Laverton North, Victoria, Australia.

    GhiasUddin, S.M. & Wilbur, S.Z. (1984a) Bioassay to determine
    biological activity of somatotropin in hypophysectomized rats.
    Unpublished report No. MR-1303 from Pitman-Moore, Inc. Submitted to
    WHO by Pharmaction Pty Ltd, Laverton North, Victoria, Australia.

    GhiasUddin, S.M. & Wilbur, S.Z. (1984b) Subacute oral toxicity screen
    of recombinant porcine somatotropin (rpST, P-3232) in rats.
    Unpublished reports No. PLR 599 and PLR 720 from Pitman-Moore, Inc.
    Submitted to WHO by Pharmaction Pty Ltd, Laverton North, Victoria,
    Australia.

    GhiasUddin, S.M., Wilbur, S.Z. & Tulla, D.A. (1984a) Intradermal
    sensitisation potential of recombinant and natural bovine and porcine
    somatotropin samples (P3229, P-3230 and P-3231, P-3232) Unpublished
    report No. PLR 662 from Pitman-Moore, Inc. Submitted to WHO by
    Pharmaction Pty Ltd, Laverton North, Victoria, Australia.

    GhiasUddin, S.M., Wolfrom, G.W., Baldwin, C.D. & Wilbur, S.Z. (1984b)
    Statistical analysis for determining bioactivity and biopotency of
    somatotropin samples. Unpublished report No. MR-1381 from
    Pitman-Moore, Inc. Submitted to WHO by Pharmaction Pty Ltd, Laverton
    North, Victoria, Australia.

    Goff, B.L., Flamming, K.P., Frank, D.E. & Roth, J.A. (1991)
    Recombinant porcine somatotropin: An immunotoxicological study.
     J. Anim. Sci., 69, 4523-4537.

    Gorman, R.L. & Sullivan, T.M. (1986) Topical sensitisation potential
    of recombinant porcine somatotropin pST P-3895 in guinea pigs.
    Unpublished report No. PLR-908 from Pitman-Moore, Inc. Submitted to
    WHO by Pharmaction Pty Ltd, Laverton North, Victoria, Australia.

    Hagen, D.R., Ziegler, H.H., Bryan, K.A. & Clark, A.M. (1989) Effect of
    exogenous porcine somatotropin (pST) on growth, reproductive
    development, and boar odour of young boars.  J. Anim. Sci., 67
    (Suppl. 1), 152 (Abstract No. 376).

    Hammond, B.G., Collier, R.J., Miller, M.A., McGrath, M., Hartzell,
    D.L., Kotts, C. & Vandaele, W. (1990) Food safety and pharmacokinetic
    studies which support a zero (0) meat and milk withdrawal time for use
    of sometribove in dairy cows.  Ann. Rech. Vet., 21 (Suppl. 1),
    107-120.

    Henry, W. (1998) Unpublished summary report from Southern Cross
    Biotech. Submitted to WHO by Pharmaction Pty Ltd, Laverton North,
    Victoria, Australia.

    Howard, D.K. & Bailey, D.E. (1989) Pivotal 15-day oral dosing study in
    rats with IGF-1. Unpublished report No. PLR 89RAT005 from
    Pitman-Moore, Inc. Submitted to WHO by Pharmaction Pty Ltd, Laverton
    North, Victoria, Australia.

    Hughes, J.P. & Friesen, H.G. (1985) The nature and regulation of the
    receptors for pituitary somatotropin.  Annu. Rev. Physiol., 47,
    469-482.

    Illi, A.H. (1989) Pilot study to determine biological half-life of
    porcine somatotropin (pST) in rats following intramuscular injection.
    Study III. Unpublished report No. PLR 992 from Pitman-Moore, Inc.
    Submitted to WHO by Pharmaction Pty Ltd, Laverton North, Victoria,
    Australia.

    Isaksson, O.G.P., Eden, S. & Jansson, J.O. (1985) Mode of action of
    pituitary somatotropin on target cells.  Annu. Rev. Physiol., 47,
    483-499.

    Joergensen, B. & Tang Soerensen, M. (1994) Porcine growth hormone for
    pigs: Effect on leg weakness and osteochondrosis.  Proc. IPVS,
    p. 280.

    Juskevich, J.C. & Guyer, C.G. (1990) Bovine growth hormone: Human food
    safety evaluation.  Science, 249, 875-884.

    Kaplan, S.A. (1965) Growth hormone.  Am. J. Dis. Child., 110,
    232-238.

    Klapper, D.G., Svoboda, M.E. & Van Wyk, J.J. (1983) Sequence of
    somatomedin-C: Confirmation of identity with insulin-like growth
    factor 1.  Endocrinology, 112, 2215-2217.

    Knobil, E. & Greep, R.O. (1959) The physiology of somatotropin with
    particular reference to its action in the rhesus monkey and the
    'species specificity' problem. In: Pincus, G., ed.,  Recent Progress
     in Hormone Research, New York, Academic Press, pp. 1-69.

    Kveragas, C.L., Seerley, R.W., Martin, R.J. & Vandergrift, W.L. (1986)
    Influence of exogenous somatotropin and gestational diet on sow blood
    and milk characteristics and on baby pig blood, body composition, and
    performance.  J. Anim. Sci., 63, 1877-1887.

    Marple, D.N. & Aberle, E.D. (1972) Porcine plasma somatotropin levels:
    Radioimmunoassay technique and its application.  J. Anim. Sci., 34,
    261-265.

    Martin, L.M. (1989) Validation of the radioimmunoassay RAM-0206 for
    porcine somatotropin in rat serum. Unpublished report No. MR-4700 from
    Pitman-Moore, Inc. Submitted to WHO by Pharmaction Pty Ltd, Laverton
    North, Victoria, Australia.

    Martin, L.M. & Yunger, L.M. (1989) Validation of the binding assay for
    porcine somatotropin (pST) using pregnant rabbit liver microsomes.
    Unpublished report No. MR-4444 from Pitman-Moore, Inc. Submitted to
    WHO by Pharmaction Pty Ltd, Laverton North, Victoria, Australia.

    Mathews, L.S., Norstedt, G. & Palmiter, R.D. (1986) Regulation of
    insulin-like growth factor I gene expression by somatotropin.  Proc.
     Natl Acad. Sci. USA, 83, 9343-9347.

    Mills, J.B., Zeringue, M., Harris, R., Wilhelmi, A.E. & Rudman, D.
    (1976) Assay of pig growth hormone preparations for metabolic
    activities in the rat and in man.  J. Clin. Endocrinol. Metab., 42,
    1127-1132.

    Molon-Noblot, S., Laroque, P., Prahalada, S., Stabinski, L.G., Hoe,
    C.-M., Peter, C.P., Duprat, P. & Van Zwieten, M.J. (1998) Effect of
    chronic growth hormone administration on skeletal muscle in dogs.
     Toxicol. Pathol., 26, 207-212.

    Nixon, S.E. & Marwer, G.E. (1970) The digestion and absorption of
    protein in man. 2. The form in which digested protein is absorbed.
     Br. J. Nutr., 24, 241-258.

    Paladini, A.C., Pena, C. & Poskus, E. (1984) Molecular biology of
    somatotropins.  CRC Crit. Rev. Biochem., 15, 25-56.

    Prahalada, S,, Srabinski, L.G., Chen, H.Y., Morrissey, R.E., De
    Burlet, G., Holder, D., Patrick, D.H., Peter, C.P. & Van Zwieten, M.J.
    (1998) Pharmacological and toxicological effects of chronic porcine
    growth hormone administration in dogs.  Toxicol. Pathol., 26,
    185-200.

    Puyt, J.-D. (1990) Hormones of the somatotropin axis: Occurrence of
    residues in edible tissues. In: Van der Wal, P., Weber, G.M. & Van der
    Wilt, F.J., eds,  Biotechnology for Control of Growth and Product
     Quality in Meat Production: Implications and Acceptability,
    Wageningen, Pudoc, pp. 157-170.

    Raben, M.S. (1959) Human growth hormone. In: Pincus, G., ed.,  Recent
     Progress in Hormone Research, New York, Academic Press, pp. 171-114.

    Sargent, R. (1998) Unpublished summary report from Pitman-Moore Inc.
    Submitted to WHO by Pharmaction Pty Ltd, Laverton North, Victoria,
    Australia.

    Schams, D.E., Kanis, E. & Van der Wal, P. (1989) Potential occurrence
    of residues after treatment of pigs with recombinant somatotropin. In:
    Van der Wal, P., Nieuwhof, G.J. & Politiek, R.D., eds,  Biotechnology
     for Control of Growth and Product Quality in Meat Production:
     Implications and Acceptability, Wageningen, Pudoc, pp. 179-182.

    Siers, D.G. & Trenkle, A. (1973) Plasma levels of insulin, glucose,
    somatotropin, free fatty acids and amino acids in resting swine.
     J. Anim. Sci., 37, 1180-1185.

    Sillence, M.N. & Etherton, T.D. (1987) Determination of the temporal
    relationship between porcine somatotropin, serum IGF-1 and cortisol
    concentrations in pigs.  J. Anim. Sci., 64, 1019--1023.

    Skaggs, C.L., Christian, L.L., Rothschild, M.F., Draper, D.D., Miller,
    L.F. & Meisinger, D.E. (1989a) Somatotropin effects on growth and leg
    traits of three stress genotypes of swine.  J. Anim. Sci., 67
    (Suppl. 1), 78 (Abstract No. 188).

    Skaggs, C.L., Christian, L.L., Rothschild, M.F., Draper, D.D., Miller,
    L.F. & Meisinger, D.E. (1989b) Somatotropin effects on quantitative
    and qualitative carcass traits of normal, carrier and stress
    susceptible swine.  J. Anim. Sci., 67 (Suppl. 1), 78 (Abstract No.
    187).

    Spence, C.A., Boyd, R.D., Bauman, D.E., Butler, W.R. & Wray, C.D.
    (1984) Effect of exogenous somatotropin on fetal energy storage and
    lactation performance in sows.  J. Anim. Sci., 59 (Suppl. 1), 246
    (Abstract No. 248).

    Sterle, J.A., Cantley, T.C., Lamberson, W.R., Lucy, M.C., Gerrard,
    D.E., Matteri, R.L. & Day, B.N. (1995) effects of recombinant porcine
    somatotropin on placental size, fetal growth, and IGF-I and IGF-II
    concentrations in pigs.  J. Anim. Sci., 73, 2980-2985.

    Sullivan, T.M. (1985) A screen primary dermal irritation study of
    recombinant porcine somatotropin (rpST) and perfect recombinant human
    somatomedin-C (p-rhSmC). Unpublished report No. PLR-767 from
    Pitman-Moore, Inc. Submitted to WHO by Pharmaction Pty Ltd, Laverton
    North, Victoria, Australia.

    Sullivan, T.M. (1987) A pilot 15-day oral gavage study of porcine
    somatotropin in rats: Effects on circulating hormone levels.
    Unpublished report No. PLR 963 from Pitman-Moore, Inc. Submitted to
    WHO by Pharmaction Pty Ltd, Laverton North, Victoria, Australia.

    Sullivan, T.M. & Atkinson, J.E. (1986) A 15-day oral gavage study in
    rats with P-3895 (pST). Unpublished report No. PLR 909 from
    Pitman-Moore, Inc. Submitted to WHO by Pharmaction Pty Ltd, Laverton
    North, Victoria, Australia.

    Tavakkol, A., Simmen, F.A. & Simmen, R.C.M. (1988) Porcine
    insulin-like growth factor-I (pIGF-I): Complementary deoxyribonucleic
    acid cloning and uterine expression of messenger ribonucleic acid
    encoding evolutionarily conserved IGF-I peptides.  Mol. Endocrinol.,
    2, 674-681.

    Terlouw, S.L., Reike, A.R., Cantley, T.C., Miller, L.F. & Day, B.N.
    (1991) The effects of recombinant porcine somatotropin on reproductive
    function in gilts treated during the finishing phase.  J. Anim. Sci.,
    69, 4294-4298.

    Toner, M.S., King, R.H., Dunshea, F.R., Dove, H. & Atwood, C.S. (1996)
    The effect of exogenous somatotropin on lactation performance of
    first-litter sows.  J. Anim. Sci., 74, 167-172.

    Wallis, M. (1975) The molecular evolution of pituitary hormones.
     Biol. Rev., 50, 35-98.

    Xian, C.A. Shoubridge, C.A. & Read, L.C. (1995) Degradation of IGF-I
    in the adult rat gastrointestinal tract is limited by a specific
    antiserum or the dietary protein casein.  J. Endocrinol., 146,
    215-225.
    


    See Also:
       Toxicological Abbreviations