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THE ROLE OF GROWTH HORMONES Colin G. Scanes IN THE DOMESTIC FOWL and Samuel J. Bowen Department of Animal Sciences Rutgers - The State University New Brunswick, NJ 08903 Send all correspondence to: Dr. C. G. Scanes Department of Animal Sciences Cook College Rutgers University New Brunswick, NJ 08903 i 42 The phenomenon and intricate and environment physiological of growth control. of The systems the factors. animals on the hormonal attention to poultry. expression into appears of those of to control be involved review of growth a whole panapy growth. These hormones presumed major importance less importance. The major (A) Growth Hormone (B) Thyroxine and other together The present knowledge There in domestic hormones animals include the with endocrine will summarize in meat genetics, and other with nutrition intrinsic for (somewhat and those which state of particularly required can be assigned complex the present species, of hormones affecting is under the full arbitrarily) are essential but of growth are: (GH) (T4)/Triiodothyronine (T3) (C) Somatomedlns (D) Steroids while (Androgens, those of perhaps (a) Specific Growth less growth Factor, Estrogens and Glucocorticoids) importanc e include: factors (e.g. Epidermal Growth Factor, EGF, Nerve NGF) (b) Insulin (c) Prolactin (d) Vitamin D metabolites Due to obvious restrictions in space consideration will be limited to GH, T4/T 3 and somatomedins. GROWTH Growth located trophs in are hormone (GH) the anterior further is produced pituitary separated HORMONE by gland. spacially 43 somatotrophs (acidophilic In the domestic being situated fowl, only in the the cells) somatocaudal portion of the anterior GH is relatively protein a single is released lation by hypothalamic I from secretory on growth and intermediary Hypothalamic Control peptide releasing hypothalamic bodies in modified to specific released releasing statin two factor (SRIF) portal pituitary peptidergic a peptidergic chickens, TRH modified in been vivo tripeptide, domestic fowl Recently, polypeptides after to exert blood of stimu- specific with down the eminence. for hormone inhibiting cell axon to In response the factors rapid in vitro has been even be very (Harvey found to supporting GRF activity 44 vary were a GH; and which importance between are direct are in et ai.,1978). be present SomatoGH of the three In young stimulating Furthermore, in hypothalami physiological GH- inhibits species. effective isolated these (TRH). While factor as to the relative to 1979) The in neurosecretory allowing factors releasing established (Jackson, neurotransmitters. stimulation), vessels is controlled gland. may TRH, of GH transported nervous importance and by in the median release Their relative are releasing factors. has 190 structure stream the secretion synthesized factors direct there is still controversy both are (GRF), and thyrotropin is the tertiary the blood directly terminals release, release also The the hypophyseal are GH is a (approximately The GH then acts hormones, factors (including to the anterior There examined, of metabolism. and (neurosecretory) stimuli into transport factors hypothalamus. nerve into chemistry of GH Secretion hypophysiotropic the residues that maintain factors. 1979). The and mammals amino-acid granules As with all adenohypophyseal by of bridges releasing (Joza et al., In all birds chain and 2 disulfide GH. GH effects gland well established. containing amino-acids) pituitary role for and characterized GH the from TRH. from human pancreatic independently tumor and rat, pig, by the laboratories availability of the response of chickens observed be to these of Roger mammalian GRF and other stimulated human, and Guillermln preparations birds to GRF. and in vitro in vivo ovine hypothalamic and of Wylie has enabled Indeed sources Vale. The examination GH secretion by mammalian GRF of has been (Scanes et i al., 1984a)). This The observation synergistic control of GH is circumstancial that the effects (i.e. with system. release There evidence than additive is also evidence fowl. Not 1982; Mikami et al., synthetic mammalian The either (Harvey ability poultry of or et al., TRH to other domestic of GH in young not in effective 1981; Decuypere secretion conscious and in cattle 1977; Klindt et al., In addition evidence In the domestic 1978) SRIF effect present in 1982; DiScala-Guenot the GH response is not or in TRH adult embryonic Furthermore it is uniformly For instance to TRH observed elevates male chicks although ineffective peptidergic of fowl, epinephrine et al., from the neurosecretory (Rabii release and anesthetized 1983). three involvement (Buonomo release interesting an inhibitory and Yamada, are TRH in sheep plasma birds (Scanes in but is et al., stimulates (Davis GH et al., 1979). role GH exist. secretion an is endogenous SRIF reduces animals. roosters (Johke, to the for the GH chicks Scanes, suggests may 1978). evoke concentrations GRF GRF on GH effects) only (Blahser, administration avian that SRIF exerts the avian hypothalamus 1984) but also an of TRH and mammalian greater in the domestic that 1984) specific presumably 1981). by 45 exerts affecting In addition It factors, neurotransmitters norepinephrine terminals. et al., releasing is probable in GH is strong secretion. a stimulatory GRF/TRH serotonin that there or appears central SRIF release to inhibit neurotransmitters may effect GH release of the pituitary both at the level of the hypothalamus and by direct action cells. II Role of GH It would be growth promotion. humans but is availability growth In GH it cost, efficiency for evidence farm sheep there In mammals, been the plasma the major case of species? been the few growth have been selected rate (e.g. attempts for growth. relationship or no studies of the fowl stimulate to improve related to growth in chicks selection that et al., examine the growth of individual has affected plasma porcine and of also hormone of GH limited on and Scanes et al, GH to pigs and to improve the rate of any farm species In between growth are cell sensitivity poor there and GH several the in dramatic It might studies (B) the plasma levels mice, concentrations can be used to advance in chicks, is (reviewed growth of effect there of GH. 1983). correlative relationship This evidence probably problems for growth concentrations In these 1982). and is that (Machlin,1972). Palmiter to GH to genes for rat or human GH to the genome have resulted the of rodents administration to role Due domestic found no attempts for high the farm have of feed conversions selection that that GH is required has There have been assume the animals. the to to is certainly true meat circumstantial ovine This and in 1984b). reasonable be addition of increases on noted of GH that in was either (e.g. Burke arguments: by there chickens a negative and Marks, (A) GH is not concentration of GH is so variable predictors performance to GH. These of authors and (C) tend to believe the second position. The action of GH in rodents this latter via increasing is to stimulate cartilage 46 growth. growth Assuming of muscles and bone, as is likely, a similar role in farm via species, intermediary tomedins on it may hormones cartilage be (the and questioned whether somatomedins). hence bone GH GH growth. is acting appears The directly to! act actions of via GH or soma- on muscle i growth may involve both direct effects on amino-acid uptake and protein ! synthesis and indirect Not only metabolism decrease does to GH 1977). "demand" for In via somatomedins result decrease lipogenesis e__tal., effects in somatic carcass (Harvey addition nutrients GH may by exclusively affecting lipogenesis and lipolysis). the "supply" modified tropin thyroi d amino-acids. or releases hormones, thyroid T4 into the liver and various of the Figure will thyroid I). exclude hormone, However consider natal chicks. is growth. 1973) and (this Furthermore, that GH and bone acts lipolysis utilization I by and other and of tissue to (Harvey increasing rather metabolites a distinct between when thyroid than (through of role thyroid (T3) hormone, T4/T 3 per to be an active ii beingi!summarized and and to T3 at s__ee.The present hormones are thyro- synthesizes then monodeiodinated ! T3 appears growth form in review and will of T4 and T 3. thyroid function administration is particularly replacement 47 the T4 is sites. triiodothyr0nine the pituitary (TSH), physiology goitrogen this (T4) The peripheral reduced For instance, increase nutrient influence of the physiology severely and to intermediary HORMONES stream. have affec£s evidence muscle hormone the relationship (King and King, skeletal the T4, T4 may other aspects Growth other affect cell proliferation. is for fatty acids stimulating the blood 1977) thyroxine Under it also There growing THYROID The growth, lipid. et al., including is disrupted reduces apparent therapy with growth for both T4 in postin chicks muscle leads to and full recovery of all administration but only David for of it it the is chicks. with et al., Further evidence be enhanced be normal that is also if chicks and its the major 2). Thus Plasma within growth of it might rates of T3 in the 1980). hormone This GH i be growth. Evidence dwarf also of GH and T4, of (Figure ppm rate can 4). It restored due is diphasic to by T3 T 3 are 2-4). reduced post-natal plasma activity. see Figure been (dw) an isolated that growth secretion. For growth in T3 increasing It, therefore, growth is T3 and (or bell-shaped) concentrations range, of T3 are low in the embryo (e.g. Decuypere and Scanes, monodeiodinase prior possible growth or concentrations may affecting that growth suggests not at T3 and growth speculated affecting elevated diet endogenous of liver monodeiodinase plasma abhorrantly studies concentration 1984b; to some, of T3 can growth. concentrations hatching. chicks have if leads sex-linked is the observation due to the lack of peripheral embryonic dwarf is between be with Similarly these stimulate circulating reduced (May, In directly studies 1973). chicks 1969) to T3 thyroid for optimum the normal to is (Marsh et al., reducing the dose-relationshlp be adjusted T4 of sex-linked growth type rate that (Figure series or elevated administration broiler appears a King, (King, to T3 in order normal only but the growth to whether profile normal and hypophysectomized of this T3 deficiency Not metabolic that from (King 1983) this being due to reduced noted optimum instance as of by T3 administration treatment. below growing converted comes (Scanes might unclear An endocrine T3 deficiency growth restoration is first latter of T4 to slow a partial King whether aspects It is and development. 48 that which T4 while those 1983). This is obviously does not develop exerts distinct of T 4 are until effects just on Considerable function that attention in avian had a has species. high been Cole incidence of given to genetic (1966) developed autoimmune variation an obese in strain thyroiditis. thyroid of leghorns Chickens with this has been i disease have reported been extensively that specifically and Pethes (1974) to TSH while response study studied reported Naked Neck to TSH. indicates regulates that Bantams (1981) a model. thyroid carried catalogued it is not found One function carried Translavanians Somes that as single in avian a dominant TSH in diverse gene species. gene a recessive the gene gene but Fodor for response for a blunted lack of fowl populations. further Two other i i single genes exist that involve chickens homozygous for the atrophy" attributed to overwork higher gene metabolism (Hutt, hypothyroidism elevated for for that function even described by reported Line Marks body 1968; the Rajaratnam et al., Marks, 1973). for et al to maintain body temperature •, Also, T4 to lower (1969), et sex-linked al. in Stewart effects For effects (1983) i ' triiodothyronine defect T3. state. the its dwarfing genetic in thyroid function They that had an "exhaustive a trend and through reported (T3) levels Washburn autosomal toward dwarf the monodeiodinase on metabolism the by lower via dwarfing (1982) thyroid genes levels was by Howarth and T4 1983). found 18 generations 1971) a In show Scanes gene manifested in the heterozygotic differences weight suggested with manner. the thyroids 1935). 1975). coupled of in a less direct to manifest Brown, conversion the dwarfing (Scanes (1972, and gene, Aberle, suggested and function in the effort and (T4) levels homozygotes responsible suggested (Grandhi thyroxine dwarf frizzling (Landauer 1959) has been thyroid Japanese on 0.2% hyperplastic 49 in birds dietary thyroid was studied quail selected thiouracil glands when for four-week (Marks and Lepore, comPared i to quail selected the on a goitrogen goitrogenic histological selected free diet or non-selected response to examination on the of the thiouracil and Washburn status lines suggest these that chickens to the non-selected estimated were hormones The in indicate Studies 1311 lines May and Bowen in while and had of Burke differences of studies uptake that are hypothyroid hormones heritable by studies Randombreds. thyroid studies act in and Hansson, (1984) found that in been and Marks in thyroid Marks (1983) when compared and Washburn (1984 b) six-week old chickens. T3 concentrations were T4 essen- when (.ippm T3) enhanced cockerels (Figure 4). Injections shank length suppression (Figure of growth sex-linked treatment body dwarfs (Figure 3,4). When in sex-linked growth hormone (200 promotion T3 (.Ippm) in growth dwarfs _g/kg) while on growth of was body in by T3 and cGH study there body interaction. 50 to (native) were was effects weight neither nor thyroid et 1966). white al., Bowen Leghorn (Figure 3). dwarf white Leghorn growth hormone affect body administered overcome The weight together (Figure of T3 was enhanced (Marsh et al., was normal chicken did not cockerels promoting fed and (Simpson, and Asling, weight itself hormone growth sex-linked of purified by T3 in normal the growth that and Riekstniece given 4). In another growth the suppression weight) Hormones suggest 1973; treatment I00 _g/kg a rat there (cGH, was and Thyroid the synergistically Thorngren al., Hormone cockerels the diet. for body weight moderately of Growth Several et reduced quail. Canadian for was In these not heritable. Interactions 1950; Japanese Athens measured (1984 a) further selected heritabilities concentrations tially of as thyroid containing (1982) and Bowen in thiouracil controls. 3). same or the In by cGH 1984 a ), T4 stimulated a main a bGH effect of bovine by treatment T4 There are at least three interact (see Figure I). One evidence that thyroid status GH (Harvey, 1982; discussed release adult earlier, in young chickens thyroidecScanes, level Chiasson levels at is at the which _evel is reciprocally et al., GH and of the pituitary related 1979; Scanes, et that tomized are (Scanes 1981) The by somatomedln GH Harvey and Scanes, release from secretion of Also, 1981) dwarfs interaction may the liver. as hormone and unpublished or are sex-linked thyroid is growth et al., can there 1976). mediates 1981; (Harvey et al., data). of GH mediated al., anesthetized (Harvey unpublished et al, system since to pituitary thyrotropin-releasing-hormone chickens the thyroid in data), (Harvey occur at and the In the rat thyroid I hormones have been shown to be necessary for normal production of somatomedins i (Burnstein, with et al., 1979). Finally, the interaction GH may be at the level of the growing cell. of the The first thyroid system two possibilities i appears there unlikely was no in view of the increase of study either GH of Bowen or et al., somatomedin C (1984). in In this chickens study following treatment. Genotype by Environment/Hormone When genetic complications of various components. by environment One Interaction traits can arise in partitioning and environmental of genotype analysis Treatment in a population the variance of these interactions. components complications These is made into several genotypic is the possibility interactions have been dlffi- i cult to show, especially a component detail of in poultry, the phenotypic with which a genotype and consequently variance. Falconer by environment are usually (1981) interaction neglected suggested that can be studied as the is re- i lated to the specificity In studies physiological of genotype of the environment by environment differences between interactions, their 51 in which genotypes indlviduais using animals is better are reared. in which understood the should direct in the investigator his experimental definite genotype thyroid defi- in deciding what environment. by clent Based environment genotypes specific on manipulation this interactions in environments in with should premise, we chickens from or without be made are showing normal dietary or thyroid hormones. Bowen et al., T 3 (O.Ippm) 3,4). In second was improved these environment (1984) experiments (Denver, expressed as broiler-type stocks than in the first study. both genotypes but observations are deficient. replacement agriculture researchers interactions. environments of More in In these The higher a lesser Scanes are specific such from both more favorably (ippm) suppression studies sex-linked genotypes dose dwarf that In a of dietary at a higher growth by interaction and normal sex-linked responded (Figures of variance. the (1983) broilers. supported dwarf to in the the chickens hormone chickens. studies. swamped definition studies the dwarf dietary genotype in the magnitude by environment genetic they in the by environment of T3 caused in chickens they design, T3 was given dose diet, cockerels by analysis studies, degree than normal in factorial genotypes et al., Leghorn genotype and the dietary be that genotype because the to a control dwarf significant between Therefore, and in a 1984) hormones environment It may well in to thyroid earlier T3 al., effect. were of conducted was highly et compared in sex-linked a difference triiodothyronine's Measurement that when growth interaction study found may interactions They by may not non-definable and uncover control many of are commonplace be observed main the genotype by effects and genotypes and by environment interactions. SOMATOMEDINS There are two somatomedins: - insulin-like 52 growth factor (IGF) I and II. These are liver polypeptides (and probably combination to Somatomedin homologous activity to 7600) organs) and carrier protein(s). C (thus which are transported in The synthesized the blood concensus A and rat by the stream in is that IGF I/SmC may be appropriate) Somatomedln to have the received lack radioi_munoassay chickens human weight IGF I while multiplication IGF II stimulating (MSA). Somatomedins largely other with _a specific is identical is (molecular has (Huybrechts of scant assay been systems. validated et al., attention Recently for 1984). in sheep domestic animals human Somatomedin a (Underwood Circulating et al., concentrations 1982) due C and of Somatomedin i C increases in (approximating trations linked of Somatomedin and of the physiology somatomedins of the physiology even programs C that and/or in (assuming six and GH levels also). following protein deficient twelve Moreover, chicks (see The availability should rapid facilitate release II selection for high be IGF progress of and in Figure of_assay in other circulating incorporated I and/or IGF II 5 poultry results sexfor systems knowledge II. concentrations into age ilplasma concen- and in the role of IGF I and for could weeks hypophysectomy, of somatomedins). selection IGF between reduced of somatomedin possible Somatomedin a maximum C are chickens, and purified is to the time for maximum dwarf summary chickens It of breeding in growth enhancement). Conclusions Attention has been given to the roles and somatomedins made to hormones. in the regulation pharmacologically These attempts of growth elevate have of growth hormone, been 53 in chickens. circulating through thyroid Attempts concentratlons !l treatment of animals hormone, have been of with these the hormone itself hormone. being or treated. drugs. transfer of More or some should Genotypes may techniques requirements availability or attention Manipulation hormone hormone of may prove drug be directed respond hormone Genetic for clearance. to differently function more practical function. drug to bring by of the technology. 54 the release genetics to treatments classical of of would would also the growth the with genetic than pharmacological manipulation It about avoid improve animal hormones or gene manipulation governmental widespread FIGURE 1 A diagramatic secretion representation of the control and the role of the thyroid 55 of thyroid hormones hormone in growth. Figure 1 THYROID HORMONES-THEIR CONTROL AND ROLE IN GROWTH 56 FIGURE 2 Diagrammatic representation concentration Body weight and growth and plasma of the relationship (body weight) of that in the controls treated). Plasma X. dwarfs A, and following 1980 where @ concentrations _, compared @ Marsh T4 was administered 1984 b control m" or dwarf chicks administered of T3 were to control and Bowen or dwarf 57 Data e__tt a__l.,1984 b where or dwarf et al., as a in sex linked _,@,@, calculated from May, _ chicks; T3 was administered chicks. T3 non-T 3 or T4 changed to non-dwarfs to control @ are expressed (i.e. nondwarfs, T4 or T 3 administration. plasma in chicks. T3 concentrations percentage between Marsh et al to 1984 wherei T3 was also 58 FIGURE 3 The effect of dietary T3 (.01 ppm), chicken or both T3 and chicken GH on body weight Cornell Leghorns. K strain white 59 GH (I00 _g/kg/day) at 5 weekslof age in Figure 3 ,, Body WT. at ._week# 400 l"] CONTROL E_T, [] GH • GH + Tll 380 l'_z _ ",IP° ° ° °oo°° °o. (g) _ii ':':':-:-:':-:-1 :.............. , 340 ,°°°°°°°°°°°o°°, ,_ ,_\\\\'_ bbb,\, \\\\\_ .o ,....:...:...:.: ::::::::::::::': ...... ...., iiiiiiiiiii i_ i:i:i:i:i:i.'.::i: ".::'::.':.':::': ,\\\\\\ ..... ,\\\_: _:_: i!iiiiiiiiiii!ii .............., -.-.-.-.:.:.-.-, .-.-.-.....-.-., 300 ..... c,.\\\\\\\\_ K 60 FIGURE 4 The effect of dietary both T 3 and chicken linked dwarf white T 3 (.01 ppm), chicken GH on body weight Leghorn 61 males. GH (i00 _g/kg/day), at 5 weeks of age in sex- or i Figure 4 320 Body WT ot 5weeks CONTROL 300 I_ T_ [] 6H EE GH+T I 62 FIGURE 5 A diagrammatic production representation of the control and the role of somatomedins 63 of somatomedin in growth. lUJ -l- IP Z 0_06 i , ' -.j "I - _l 64 References Blahser, S. 1982 Topography, ontogeny and functional aspects of immunoreactive neuropeptide systems in the domestic fowl. In: Avian Endocrinology, Environmental and Ecological Perspectives, (Mikami S, Homma K and Wada M, eds.) pp. 11-24, Sprlnger-Verlag, Berlin. Bowen, S.J. and K.W. stress in chickens In Press. Washburn, 1984 a Thyroid and adrenal response to heat and quail differing in heat tolerance. Poultry Sci. Bowen, Washburn, S.J. and function In Press. Bowen, K.W. 1984 b. in Athens-Canadian S.J., L.M. Genetics Randombred Huybrechts, J.A. of heat chickens. Marsh, and C.G. Appl, Scanes, 1984. Trilodothyronine interacts with growth hormone and regulation in dwarf and normal chickens: Submitted Buonomo, F.C., N.G. Zimmerman involvement in the control Gen. Comp. Endocrinol. (In Burke, W.H. and H.L. Marks non-selected broiler Growth 46:283-295. Burke, W.H. and H.L. triiodothyronine weight. Poultry Burstein, P.J., B. and C.G. Scanes, of growth hormone Press). 1982. lines Marks Growth and 1984. Growth levels of Japanese Science 63:207-213. Draznin, C.J. from Johnson, Cole, R.K. 53:1021. Davis, 1966. S.L., M. Hereditary S. prostaglandins and growth Decuypere, Anflnson, and in wether E. and C.G. prolactin to eight D.S. for in of age. and four-week Schalch, hormone, factor, levels weeks 1979. body The effect the growth hormoneand its carrier protein Klandorf, C.G. Scanes and S. Harvey, 1979. The methlmazole on levels of plasma hormones in Poultry Sci. 58:1575-1583. hypothyroidism and D.L. Ohlson thyrotropin releasing lambs. 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Metallothionein-human GH fusion genes stimulate growth of mice. Science 222:809-814. 67 Rabii, J., Buonomo, F and Scanes, C.G. (1981). Role of serotonin in the regulation of growth hormone and prolactln secretion in the domestic fowl. J. Endocr. 90:355-358. Rajaratnam, G., Selvarajah,T., and J.D. Summers, thyroprotein on growth rate of dwarf pullets. 1770. 1969. The effect of Poultry Sci. 48:1768- of growth Riekstniece, E. and C.W. Asling, 1966. Thyroxine augmentation hormone induced endochondrol osteogenesis. Proc. Soc. Exp. Biol. Med. 123:258-263. Scanes, C.G., L. Gales, Endocrine Endocrin. Scanes, S. Harvey, studies in young 30:419-423. C.G., Harvey, A. Chadwick, chickens S., Morgan, B.A. and W.S. of the obese Newcomer, strain. and M. Haynes, 1976. Gen. and Comp. 1981. Effect of synthetic thyrotrophln-releasing hormone and its analogues on growth hormone secretions in the domestic fowl (Gallus domesticus). Acta Endocrinol. 97:448-453. Scanes, C.G., J.A. Marsh, E. Decuypere, and P. Rudas the plasma concentrations of thyroxine, in sex-linked dwarf and autosomal dwarf domesticus). J. Endocr. 97:127-135. 1983. Abnormalities in triiodothyronine and growth hormone White Leghorn domestic fowl (Gallus Scanes, C.G., R.V. Carsia, T.J. Lauterlo, L. Huybrechts, J. Rivier, and W. Vale (1984a). Synthetic human pancreatic growth hormone releasing factor (GRF) stimulates growth hormone secretion in the domestic fowl (Gallus domesticus). Life Sci. 34:1127-1134. Scanes, C.G., S. Harvey, J.A. Marsh, and D.B. King, growth in poultry. Poult. Sci. (In Press). Simpson, M.L., C.W. Asling, and H.M. Evans, on skeletal growth and differentiation. 1984b). Hormones and 1950. Some endocrine influences Yale J. Biol. Med. 23:1-27. Somes, Jr., R.G., 1981. International registry of poultry genetic stocks. Storrs Agricultural Experiment Station Bulletin 460, The University of Connecticut, Storrs, Connecticut. Stewart, P.A. and K.W. Washburn, (T_) and triiodothyronine Scl. 61:1550. 1982. Characterization (T3) levels as affected of serum thyroxine Poultry by the dw gene. Thorngren, K.G., and L. I. Hansson, 1973. Effect of thyroxine hormone on longitudinal bone growth in the hypophysectomized Endocrinol 74:24-40. and growth rat. Acta Underwood, L.E., A.J. D'Ercole, K.C. Copeland, J.J. VanWyk, T. Hurley, and S. Handwerger, (1982). Development of a heterologous radioimmunoassay for somatomedin C in sheep blood. J. Endocrinol. 93:31-39. 68 THE ROLE OF GROWTH HORMONES Questions i. IN THE DOMESTIC FOWL and Answers Ruth Shuman You have established a clear planned or in progress i.e., in cell or organ trend with involving culture? in vivo the examination studies, do you have of these hormones studies in vitro C.G. Scanes We are examining effects of releasing in primary culture and of GH on liver 2. factors on anterior pituitary and adipose tissue in vitro. cells Terry Wing Wouldn't you expect a fast growing broiler to have and expect it to be bound to receptor sites? low plasma levels of GH C.G. Scanes I would suggest that one reason why fast growing, broiler chickens do not have elevated levels of GH in their plasma is due to increased sensitivity of the tissues to GH. It is possible that this is due to increases in the number or affinity of GH receptors. 3. G. Havenstein If I recall correctly, you stated that animals with an elevated growth rate have elevated levels of Somatomedin C. Have you compared the Somatotropin C levels in the Athens - Canadian Randombred Broiler Strain with the levels in some of our modern broiler strains to see if this relationship holds true? Dr. C.G. Scanes We have not examined 4. this interesting question at this time. Dr. Ira Carte Could you please elaborate on growth hormone receptors? C.G. Scanes While GH receptors have been examined in many mammalian published reports as yet on GH receptors in poultry. 69 species, there are no