Purification and radioimmunoassay of chicken growth hormone

Research Note: Development of a sandwich ELISA for determining plasma growth hormone concentrations in goose

Growth hormone (GH) is required for normal postnatal development in poultry; however, no immunoassay exists to assess its levels in geese plasma, hindering the study of endocrine regulation in this species. We developed a sandwich ELISA to determine the GH concentrations in the plasma of geese. Recombinant goose GH was produced using a eukaryotic expression system and purified for use as the reference standard in ELISA and the antigen for producing the polyclonal antibodies in rabbits. Rabbit anti-goose GH polyclonal antibody was used to coat the wells of the ELISA plate, and its biotinylated form served as the detection antibody. An avidin-conjugated horseradish peroxidase was used to bind the detection antibody and catalyze the chromogenic reaction of 3,3,5,5-tetramethylbenzidine and H₂O₂. A sigmoidal curve was fitted to the optical density and the log of the standard GH concentration using the four-parameter logistic model. The sensitivity of the assay was less than 0.156 ng/mL. The intra- and interassay coefficients of variation were less than 9 and 13%, respectively. The response curve of the serially diluted plasma samples from geese exhibited a good parallel relationship with that observed for the reference standards. The assay effectively detected differences in GH concentrations in plasma samples from geese at various physiological stages; thus, it will be useful for future study of their growth and metabolism.

Secretagogue induction of GH release in QNR/D cells: prevention of cell death

Retinal ganglion cells (RGCs) in the chick embryonic neural retina are extrapituitary sites of growth hormone (GH) synthesis and release. The regulation of GH secretion by these cells is largely unknown, although we recently discovered several of the hypothalamic releasing factors involved in pituitary GH regulation (including GH-releasing hormone (GHRH) and thyrotropin releasing hormone, TRH) to be present in the cytoplasm of immortalized quail RGCs (QNR/D cells). QNR/D cells may therefore provide an experimental model for studies on GH regulation in the chick neural retina. The possibility that GHRH and TRH might stimulate GH secretion in QNR/D cells was therefore investigated. Both peptides acutely depleted the GH content of the QNR/D cells, as demonstrated by immunocytochemistry and ELISA, whilst increasing the GH content in incubation media. Both peptides also increased the immunochemical and ELISA content of the QNR/D cells and the content of GH in the incubation media after long-term incubation. Cell survival, determined by metabolic activity of the QNR/D cells and by TUNEL-labeling, was reduced when the endogenous GH content was reduced by GH immunoneutralization, even in the presence of exogenous GHRH or TRH. Cell survival was also reduced when endogenous GHRH was blocked by GHRH immunoneutralization, although the immunoneutralization of endogenous TRH did not affect QNR/D cell survival. In summary, these results demonstrate secretagogue actions of exogenous GHRH and TRH on the secretion of GH from QNR/D cells. They also suggest that endogenous GHRH, but not endogenous TRH, prevents cell death by increasing endogenous GH secretion in QNR/D cells.

Growth hormone (GH) and GH-releasing hormone (GHRH): Co-localization and action in the chicken testis

Growth hormone (GH) gene expression is not confined to the pituitary gland and occurs in many extrapituitary tissues, including the chicken testis. The regulation and function of GH in extrapituitary tissues is, however, largely unknown. The possibility that chicken testicular GH might be regulated by GH-releasing hormone (GHRH), as in the avian pituitary gland, was investigated in the present study. GHRH co-localized with GH in the germinal epithelium and in interstitial zones within the chicken testes, particularly in the spermatogonia and spermatocytes. In testicular cell cultures, exogenous human GHRH1-44 induced (at 1, 10 and 100nM) a dose-related increase in GH release. Western blot analysis showed a heterogeneous pattern in the GH moieties released during GHRH stimulation. 26kDa monomer GH was the most abundant moiety under basal conditions, but 15 and 17kDa isoforms were more abundant after GHRH stimulation. GHRH treatment also increased the abundance of PCNA (proliferating cell nuclear antigen) immunoreactivity in the testes. This may have been GH-mediated, since exogenous GH similarly increased the incorporation of ((3)H)-thymidine into cultured testicular cells and increased their metabolic activity, as determined by increased MTT reduction. Furthermore, GH and GHRH immunoneutralization blocked GHRH-stimulated proliferative activity. In summary, these results indicate that GHRH stimulates testicular GH secretion in an autocrine or paracrine manner. Data also demonstrate proliferative actions of GHRH on testicular cell number and suggest that this action is mediated by local GH production.

Growth hormone and growth?

Pituitary GH is obligatory for normal growth in mammals, but the importance of pituitary GH in avian growth is less certain. In birds, pituitary GH is biologically active and has growth promoting actions in the tibia-test bioassay. Its importance in normal growth is indicated by the growth suppression following the surgical removal of the pituitary gland or after the immunoneutralization of endogenous pituitary GH. The partial restoration of growth in some studies with GH-treated hypophysectomized birds also suggests GH dependency in avian growth, as does the dwarfism that occurs in some strains with GHR dysfunctions. Circulating GH concentrations are also correlated with body weight gain, being high in young, rapidly growing birds and low in slower growing older birds. Nevertheless, despite these observations, there is an extensive literature that concludes pituitary GH is not important in avian growth. This is based on numerous studies with hypophysectomized and intact birds that show only slight, transitory or absent growth responses to exogenous GH-treatment. Moreover, while circulating GH levels correlate with weight gain in young birds, this may merely reflect changes in the control of pituitary GH secretion during aging, as numerous studies involving experimental alterations in growth rate fail to show positive correlations between plasma GH concentrations and the alterations in growth rate. Furthermore, growth is known to occur in the absence of pituitary GH, as most embryonic development occurs prior to the ontogenetic appearance of pituitary somatotrophs and the appearance of GH in embryonic circulation. Early embryonic growth is also independent of the endocrine actions of pituitary GH, since removal of the presumptive pituitary gland does not impair early growth. Embryonic growth does, however, occur in the presence of extrapituitary GH, which is produced by most tissues and has autocrine or paracrine roles that locally promote growth and development. The role of GH in avian growth is therefore still unclear.

Growth hormone expression and neuroprotective activity in a quail neural retina cell line

We have previously shown that growth hormone (GH) is produced within cells of the chick embryo retina where it appears to act as an autocrine/paracrine anti-apoptotic factor in the regulation of programmed cell death during retinal development. These investigations were carried out on cultured chick embryo retinal ganglion cells (RGCs) as well as on the chick embryo retina in ovo, using GH protein knock-down by immunoneutralization. We have now investigated the putative neuroprotective actions of GH using a quail embryo neural retina cell line (QNR/D) treated with GH siRNA to silence the local synthesis of GH. We now show that knock-down of GH by gene silencing in cells of this cultured embryonic neural retina cell line, using NR-cGH-1 siRNA, correlates with the increased appearance in the cultures of cells with apoptotic nuclear morphology. This result is consistent with our previous results using protein knock-down by immunoneutralization. We thus validate, using different technology and a different culture system, our contention that GH, produced locally by cells of the neural retina acts in an autocrine or paracrine manner to regulate cell survival in the retina.

Retinal ganglion cell survival in development: mechanisms of retinal growth hormone action

Several variants of growth hormone (GH) are found in the retina and vitreous of the chick embryo, where they appear to act as cell survival factors, having neuroprotective effects on retinal ganglion cells (RGCs). Here, we investigate the molecular mechanisms of the anti-apoptotic effect of GH in cultured RGCs. GH treatment increased Akt phosphorylation in these cells, which is an anti-apoptotic event. Whereas unphosphorylated Akt was detected in both nucleus and cytoplasm of RGCs by immunocytochemistry, the phosphorylated form of Akt (Akt-phos) was located primarily in the cytoplasm of both normal and apoptotic cells, although levels were markedly lower in the latter. It was found that GH treatment of RGCs reduced Akt levels, while concomitantly raising Akt-phos levels, consistent with a role for Akt signaling pathways in GH neuroprotective action. This was substantiated using Wortmannin, which, like GH antiserum, inhibited Akt phosphorylation and initiated apoptosis. The addition of Wortmannin to RGC cultures simultaneously with GH significantly reduced the anti-apoptotic effect of GH. The induction of apoptosis by GH antiserum was clearly accompanied by an increase in caspase-3 activation and PARP-1 cleavage, both of which were significantly reduced in the presence of the broad spectrum caspase inhibitor, Q-VD-OPh, which itself had a dramatic neuroprotective effect on cultured RGCs. Calpain activation appeared to be a major caspase-independent pathway to PARP-1 cleavage and apoptosis in these cells. Calpain inhibitor III (MDL 28170) was able to reduce PARP-1 cleavage and abrogate the apoptogenic effect of GH antiserum. The results support the view that caspase and calpain inhibitors are major neuroprotective agents for RGCs, and that pathways that activate both caspases and calpains are important for the anti-apoptotic actions of GH in these cells.

Retinal growth hormone is an anti-apoptotic factor in embryonic retinal ganglion cell differentiation

Cells of the neural retina in the chick embryo undergo several waves of apoptosis during development, including peaks at approximately embryonic day (ED) 7 and 12. Prominent among the cells involved in these phases of cell death are the retinal ganglion cells (RGCs). We have previously shown that growth hormone (GH) is expressed in the neural retina, and particularly, in the RGCs. Here we study the ability of GH to rescue retinal cells from apoptosis, both in vitro and in vivo. When retinas from embryos at ED 6-8 are explanted on collagen gels, the application of recombinant GH, at 10(-6)m, significantly reduced the incidence of apoptotic cells in the cultures as judged by terminal deoxynucleotide transferase-mediated dUTP-biotin nick end labelling (TUNEL). GH was delivered to neural retinas in ovo, by microinjection into the eye cup at ED 2. When these embryos were examined at ED 6-8, no reduction in cell death was observed below the normal low control levels. However, when antibodies to GH were microinjected, the incidence of cell death increased significantly at ED 6, providing evidence that in vivo immunoneutralization of endogenous GH results in triggering of apoptotic signaling pathways. Evidence that RGCs are a particular target of this neuroprotective effect of GH was provided by examination of cultures enriched for RGCs by immunopanning. In serum-free culture, RGCs, identified by anti-Islet 1 immunolabelling, were found to be susceptible to the effect of GH immunoneutralization, which approximately quadrupled the incidence of apoptosis in the cultures. We propose that GH is a naturally occurring autocrine and/or paracrine neuroprotective agent in the developing retina which is involved in the regulation of retinal cell numbers during early embryogenesis.

Heterogeneity of growth hormone immunoreactivity in lymphoid tissues and changes during ontogeny in domestic fowl

Growth hormone (GH) expression is not confined to the pituitary and occurs in many extrapituitary tissues. Here, we describe the presence of GH-like moieties in chicken lymphoid tissues and particularly in the bursa of Fabricius. GH-immunoreactivity (GH-IR), determined by ELISA, was found in thymus, spleen, and in bursa of young chickens, but at concentrations <1% of those in the pituitary gland. Although the GH concentration in the spleen and bursa was approximately 0.82 and 0.23% of that in the pituitary at 9-weeks of age, because of their greater mass, the total GH content in the spleen, bursa, and in thymus were 236, 5.18, and 31.5%, respectively, of that in the pituitary gland. This GH-IR was associated with several proteins of different molecular size, as in the pituitary gland, when analyzed by SDS-PAGE under reducing conditions. While most of the GH-IR in the pituitary was associated with the 26 kDa monomer (40%), the putatively glycosylated 29 kDa variant (16%), the 52 kDa dimer (14%) and the 15 kDa submonomeric isoform (16%), GH-IR in the lymphoid tissues was primarily associated (27-36%) with a 17 kDa moiety, although bands of 14, 26, 29, 32, 37, 40, and 52 kDa were also identified in these tissues. The heterogeneity pattern and relative abundance of bursal GH-IR bands were determined during development between embryonic day 13 (ED13) and 9-weeks of age. The relative proportion of the 17 kDa GH-like band was higher (45-58%) in posthatched birds than in the 15 and 18-day old embryos (21 and 19%, respectively). The 26 kDa isoform was minimally present in embryos (<4% of total GH-IR) but in posthatched chicks it increased to 12-20%. Conversely, while GH-IR of 37, 40, and 45 kDa were abundantly present in embryonic bursa ( approximately 30% at ED13 and approximately 52-55% at ED15 and ED18, respectively), in neonatal chicks and juveniles they accounted for less than 5%. These ontogenic changes were comparable to those previously reported for similar GH-IR proteins in the chicken testis during development. In summary, these results demonstrate age-related and tissue-specific changes in the content and composition of GH in immune tissues of the chicken, in which GH is likely to be an autocrine or paracrine regulator.

The effects of dietary vitamin E and selenium deficiencies on plasma thyroid and thymic hormone concentrations in the chicken

Beginning at hatching, male Cornell K strain single comb white leghorn chickens were fed a basal diet, with or without vitamin E (100 IU/kg) and/or selenium (Se, 0.2 ppm). After 3 weeks of treatment, animals fed either the Se-deficient or basal diet had significantly reduced plasma Se-dependent glutathione peroxidase activities when compared to those fed a vitamin E and Se-supplemented diet. Similarly, animals fed the vitamin E-deficient or basal diet had significantly reduced plasma alpha-tocopherol levels. The effect of these treatments on plasma concentrations of thyroid hormones (T(3)/T(4)), growth hormone (GH), and thymic hormone (thymulin) was determined using radioimmunoassay and ELISA. A deficiency in Se, but not in vitamin E, resulted in an increase in plasma T(4) concentrations while plasma T(3) concentrations were decreased. Plasma GH levels showed some fluctuation as a result of the dietary treatments but there was no significant correlation between plasma GH levels and any of the other variables. A significant decrease in plasma thymulin levels was observed in Se-deficient birds compared to those receiving adequate Se in the diet. A vitamin E deficiency had no measurable effect on plasma thymulin levels. From these studies, we conclude that plasma thymulin concentrations directly correlate with plasma T(3) concentrations which are negatively affected by a Se deficiency.

Chicken growth hormone: further characterization and ontogenic changes of an N-glycosylated isoform in the anterior pituitary gland

Glycosylation is one of the post-translational modifications that growth hormone (GH) can undergo. This has been reported for human, rat, mouse, pig, chicken and buffalo GH. The nature and significance of GH glycosylation remains to be elucidated. This present study further characterizes glycosylated chicken GH (G-cGH) and examines changes in the pituitary concentration of G-cGH during embryonic development and post hatching growth. G-cGH was purified from chicken pituitaries by affinity chromatography (Concanavalin A-Sepharose and monoclonal antibody bound to Sepharose). Immunoreactive G-cGH has a MW of 26 kDa or 29 kDa as determined by SDS-PAGE, respectively, under non-reducing and reducing conditions. Evidence that it is N-glycosylated comes from its susceptibility to peptide N-glycosidase F, and its resistance to O-glycosidase. Based on the ability of G-cGH to bind Concanavalin A or wheat germ agglutinin but not other lectins and its susceptibility to peptide N-glycosidase F, a hybrid or biantennary type glycopeptide (GlcNac2, Man) structure is proposed. Some G-cGH can be observed in the pituitary at most ages examined (from 15-day embryo to adult). Moreover, electron microscopy revealed the presence of both immuno-reactive GH and Concanavalin A-reactive sites in the same secretory granules in the somatotrope. There were marked changes in the level and relative proportion of G-cGH in the pituitary gland during development and growth, the proportion of G-cGH rising during late embryonic development (e.g., between 15 and 18 days of development) and with further increases between 9 weeks and 15 weeks old. G-cGH was able to bind to chicken liver membrane preparations with less affinity than non-glycosylated monomer; on the other hand, however, G-cGH stimulated cell proliferation on Nb2 lymphoma bioassay whereas the non-glycosylated monomer was uncapable to do it.

Extrapituitary beta TSH and GH in early chick embryos

Somatotropes and thyrotropes are thought to be derived from the same cellular lineage and the expression of both growth hormone (GH) and thyrotropin (beta TSH) is thought to be dependent upon the same (Pit-1) transcription factor. The presence and comparative distribution of GH- and beta TSH-immunoreactivity in early chick embryos, was therefore investigated, especially as extrapituitary GH-immunoreactive cells are present in some peripheral tissues of early chick embryos prior to the ontogenic differentiation of the pituitary gland. At the end of the first trimester of incubation (embryonic day (ED) 7), GH-immunoreactivity was widespread in the head, particularly in neural tissue. Strong labeling was found in the diencephalon and mesencephalon and in neural ganglia and the trigeminal nerve. beta TSH-immunoreactivity was also present in these tissues, although restricted to the ependymal cells lining the diocoele and mesocoele and absent from mantle layers. It was also present in the cellular layer lining the otic vesicle, which was devoid of GH staining. In contrast, Rathke's pouch, the primordial pituitary gland was without GH- or beta TSH-staining. Control sections incubated with preabsorbed antisera or with pre-immune serum were completely devoid of staining. In the trunk, the epidermal cells were stained for beta TSH, but not for GH. Intense GH-immunoreactivity was present in the ventral and dorsal horns of the spinal cord and was particularly strong in the outer marginal layer. In contrast, beta TSH-immunoreactivity was again restricted to ependymal cells lining the spinal canal, which were devoid of GH-immunoreactivity. Strong GH staining was also present in the dorsal and ventral root ganglia, both of which lacked significant beta TSH staining. In non-neural tissues, both GH and beta TSH staining was present in the crop, although in topographically different cells. beta TSH-immunoreactivity was also present in the cells lining the bronchial ducts and the adluminal linings of the pleural and pericardial cavities. GH-immunoreactivity, in contrast, was absent from the lung but present in the surrounding intracostal muscles and in the Müllerian duct. Both GH- and beta TSH-immunoreactivity was present in liver hepatocytes. These results clearly show, for the first time, the presence of TSH-immunoreactivity in central and peripheral tissues of the ED7 chick embryo, prior to the differentiation of pituitary thyrotropes. They also show that beta TSH- and GH-immunoreactive cells are differentially located within embryonic tissues.

Characterization of a bioactive 15 kDa fragment produced by proteolytic cleavage of chicken growth hormone

There is evidence for a cleaved form of GH in the chicken pituitary gland. A 25 kDa band of immunoreactive-(ir-)GH, as well as the 22 kDa monomeric form and some oligomeric forms were observed when purified GH or fresh pituitary extract were subjected to SDS-PAGE under nonreducing conditions. Under reducing conditions, the 25 kDa ir-GH was no longer observed, being replaced by a 15 kDa band, consistent with reduction of the disulfide bridges of the cleaved form. The type of protease involved was investigated using exogenous proteases and monomeric cGH. Cleaved forms of chicken GH were generated by thrombin or collagenase. The site of cleavage was found in position Arg133-Gly134 as revealed by sequencing the fragments produced. The NH2-terminal sequence of 40 amino acid residues in the 15 kDa form was identical to that of the rcGH and analysis of the remaining 7 kDa fragment showed an exact identity with positions 134-140 of cGH structure. The thrombin cleaved GH and the 15 kDa form showed reduced activity (0.8% and 0.5% of GH, respectively) in a radioreceptor assay employing a chicken liver membrane preparation. However, this fragment had a clear bioactivity in an angiogenic bioassay and was capable to inhibit the activity of deiodinase type III in the chicken liver.

GH secretion in TRH-refractory and TRH-responsive chickens is independent of somatotroph abundance and morphometry

Chicken pituitary glands chronically exposed (for 2-4 h) to growth hormone (GH) secretagogues in vitro have increased GH secretion and increased numbers of GH-secreting cells. In contrast, thyrotropin-releasing hormone (TRH)-induced GH release in chickens in vivo is only transitory and cannot be maintained by constant infusion or repeated serial iv administration. The possibility that this reflects changes in somatotroph abundance, morphology, and GH content was therefore examined in chickens responsive or refractory to TRH in vivo. TRH-induced GH release was immediately (within 10-30 min) followed by a reduction in the size and number of immunoreactive pituitary somatotrophs and in the size of somatotroph clusters, resulting in a reduction in somatotroph area. The number and area of the immunoreactive GH-secreting cells was further reduced 60 min after the bolus administration of TRH, although control values were restored after 120 min. The decline in immunoreactive somatotroph number and size was attenuated by serial TRH injections, but this did not restore plasma GH responsiveness in TRH-refractory birds. These results demonstrate that somatotroph responses to GH secretagogues in vivo differ from those in vitro.

Influence of continuous growth hormone or insulin-like growth factor I administration in adult female chickens

A series of studies was conducted to determine whether growth hormone (GH) exerts effects on adult female chickens. Recombinant chicken GH (rcGH) was administered continuously via osmotic minipumps. No consistent effects of rcGH treatment were observed on reproductive indices. Hens receiving rcGH treatment for 10 days exhibited hepatomegaly and showed a tendency (P < 0.1) for increased spleen and thymus weights. Moreover, there were increases in the circulating concentrations of insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGF-BPs) (22-kDa IGF-BP after 2, 5, and 10 days; 28-kDa IGF-BP after 5 and 10 days; and 36-kDa IGF-BP after 10 days) with rcGH treatment. To determine whether the changes in IGF-BPs were due directly to GH or indirectly via IGF-I, the effects of the continuous administration of rcGH or recombinant human IGF-I (rhIGF-I) were compared. While rcGH again elevated the circulating levels of 28- and 36-kDa IGF-BPs, no such effect was observed with rhIGF-I treatment. However, both treatments exerted similar effects in depressing pituitary GH mRNA levels and elevating plasma concentrations of IGF-I. It is concluded that GH directly elevates circulating concentrations of IGF-I and IGF-BPs, but the negative feedback effect on GH synthesis is mediated via IGF-I.

Growth hormone: a paracrine growth factor in embryonic development?

Although pituitary growth hormone is obligatory for normal postnatal growth and development, early embryonic and fetal growth is generally considered to be independent of pituitary GH. Indeed, in chickens, somatotrophs and serum GH are not detectable until late in embryogenesis, and neither partial decapitation nor pre-hatch GH administration greatly affects embryonic growth. However, since it is now known that GH can be produced and act in many extra-pituitary tissues, early embryonic growth may be independent of pituitary GH but dependent upon the paracrine actions of extra-pituitary GH. The possibility that growth hormone may be a paracrine growth factor during early development will therefore be considered in this brief review, which is based on the embryogenesis of the domestic fowl.

Quantitative studies of chicken somatotrophs during growth and development by morphometry, immunocytochemistry, and flow cytometry

Changes in the male chicken somatotroph during growth and maturation have been examined by morphometric and immunocytochemical (ICC) analysis of serial sections of the anterior pituitary gland and by flow cytometry of dispersed anterior pituitary cells. ICC showed that somatotrophs are confined to the middle and caudal thirds of the anterior pituitary gland at all ages from 5 to 26 weeks. At a given age somatotrophs are of equal size at all positions along the cephalocaudal axis of the anterior pituitary gland. However, there are age-related changes: from 5 to 11 weeks rises occur in both the mean total somatotroph volume per gland (64%) and the mean number of somatotrophs (78%), while the mean volume of the single somatotroph is unchanged. From 11 to 18 weeks the mean volume of the single somatotroph decreases 41%. From 18 to 26 weeks the mean volume of the somatotroph, the mean total somatotroph volume, and the mean number per gland do not change. Flow cytometry studies suggested that somatotrophs from adults have less growth hormone (GH) than somatotrophs from young birds. The increases in total somatotroph volume and number from 5 to 11 weeks are consistent with the rise in anterior pituitary GH reported previously. Basic quantitative morphological information about age-related changes in somatotrophs is reported here. When combined with additional facts from future work, they may explain the well-documented sharp decline in circulating GH from 5 to 11 weeks.

Effects of polychlorinated biphenyl mixtures and three specific congeners on growth and circulating growth-related hormones

Polychlorinated biphenyls (PCB) are ubiquitous environmental contaminants that bioaccumulate in avian species. Exposure to PCBs can result in decreased growth. Thyroid hormones and growth hormone (GH) are important for normal growth. The present studies employed the chicken embryo to investigate effects of Aroclor 1242, Aroclor 1254, 2,2',6,6'-tetrachlorobiphenyl (TCB), 3,3',4,4'-TCB, and 3,3',5,5'-TCB on growth and growth-related hormones. The following indices were measured: embryo mortality, body weights, bone length, pituitary GH content, and plasma concentrations of triiodothyronine (T3), thyroxine (T4), GH, and insulin-like growth factor-1 (IGF-1). Fertile eggs were injected with PCBs on Day 0 and indices determined on Day 17 of incubation. Unexpectedly, 3,3',5,5'-TCB or low-dose Aroclor 1242 treatment increased body weight and bone length (P < 0.05), whereas Aroclor 1242 (high dose), 3,3,4,4'-TCB, or Aroclor 1254 treatment reduced body weights and/or bone length (P < 0.05). Aroclor 1242 or 3,3',4,4'-TCB (low-dose treatment) elevated plasma T4 concentrations (P < 0.05). Both growth and pituitary GH content were increased (P < 0.05) by 3,3',5,5'-TCB (low dose) or Aroclor 1242 treatment. Despite marked differences in growth rates, plasma T3, GH, and IGF-I concentrations were unaffected by PCB treatment. Growth-related hormones may not be responsible for the growth depression observed after PCB treatment. Possibly the decrease in growth occurred because of general toxicity. The importance of chlorine position in causing thyroid hormone axis alterations was not clearly established.

Chronic administration of growth hormone (GH) to adult chickens exerts marked effects on circulating concentrations of insulin-like growth factor-I (IGF-I), IGF binding proteins, hepatic GH regulated gene I, and hepatic GH receptor mRNA

In young birds, growth hormone (GH) administration has been found to have only a small or even no effect on circulating concentrations of insulin-like growth factor-I (IGF-I). This is in obvious contrast to the situation in mammals. The present study examines the effect of continuous administration of GH in adult male chickens. Plasma concentrations of IGF-I were markedly elevated (2.5-3.0-fold, p < 0.001) in GH-treated chickens. There were also some transient increases in the circulating levels of IGF binding proteins. Adult chickens showed other manifestations of increased responsiveness to GH, including elevated hepatic expression of GH-regulated gene-I (mRNA) with GH treatment (p < 0.05), and a tendency (p < 0.08) for decreased GH-receptor mRNA. In contrast to the changes in circulating concentrations of GH and IGF-I with GH treatment, no changes in plasma concentrations of thyroid hormones, reproductive hormones, glucose, or nonesterified fatty acids were evident.

Expression of the growth hormone gene in immune tissues

It is well established that growth hormone (GH)-like proteins and mRNA are present in immune tissues, but it is not known whether this reflects ectopic transcription of the GH gene or the expression of a closely related gene. This possibility was, therefore, investigated. Immunoreactive (IR) GH-like proteins were readily measured by radioimmunoassay and immunoblotting in the spleen, bursa of Fabricius and thymus of immature White Leghorn chickens, in which IR-GH was similar in size and antigenicity to the major GH moieties present in the pituitary gland. RT-PCR of mRNA from these immune tissues, with oligonucleotide primers spanning the coding region of pituitary GH cDNA, also generated cDNA fragments identical in size (689 bp) to pituitary GH cDNA.BamHI andRsaI cleavage sites were located in these cDNA sequences in the same position as those in pituitary GH cDNA. These amplified cDNA sequences also contained sequences that hybridized, by Southern blotting, with a chicken pituitary GH cDNA probe, thus suggesting a high degree of homology between pituitary and immune GH transcripts. The nucleotide sequence of the PCR products generated from these immune tissues, determined by a modified cycle dideoxy chain termination method, were also identical to pituitary GH cDNA. This homology extended over 593 bp of the spleen cDNA (spanning nucleotides 70-663 of the pituitary GH cDNA and its coding region for amino acids 5-201), 613 bp of the bursa cDNA fragment (spanning nucleotides 63-676 of the pituitary GH cDNA and its coding region for amino acids 3-207) and 607 bp of the thymic cDNA fragment (spanning nucleotides 61-665 of pituitary GH cDNA and its coding region for amino acids 4-203). These results clearly establish that the GH mRNA is present in immune tissues, in which GH-IR proteins are present. The local production of GH within the immune system of the domestic fowl, therefore, suggests it has paracrine or autocrine roles in modulating immune function.

Ontogeny of pituitary and serum growth hormone in growing turkeys as measured by radioimmunoassay and radioreceptor assay

Some mammalian studies have revealed a wide discrepancy in pituitary and circulating growth hormone (GH) measurements determined by immunological and biological assay methods. Recent studies demonstrating that avian GH exists in numerous isoforms raise concerns that immunological measurement of GH may not accurately reflect the amount of biologically active hormone present. We sampled eight different male turkeys of a commercial strain weekly until 6 wk of age, and then biweekly until 20 wk. Total pituitary GH content and serum GH concentration were measured by avian GH RIA and radioreceptor assay (RRA). The highest mean serum GH concentration occurred at 3 wk, and the ontogeny of serum GH content from 1 to 8 wk was similar whether measured by RIA or RRA. Pituitary GH content was highest at 6 wk, but RIA and RRA estimates differed markedly throughout the study. Pituitary content of biologically active GH, as estimated by RRA, exceeded that of immunologically active GH from 2 to 10 wk, whereas the reverse was true at 14, 18, and 20 wk. We conclude that this avian GH RIA accurately measures bioactive circulating turkey GH, but that the pituitary of the young turkey may contain bioactive GH isoforms that have poor immunological activity in our RIA.

Angiogenic activity of anterior pituitary tissue and growth hormone on the chick embryo chorio-allantoic membrane: a novel action of GH

A useful system to evaluate the angiogenic activity of hormones and growth factors is the chorioallantoic membrane (CAM) of chick embryos. The present studies examined the angiogenic activity of chicken anterior pituitary glands and both fibroblast growth factor (FGF) and growth hormone (GH). Grafts of anterior pituitary gland evoked an angiogenic response on the CAM which was lost if the adenohypophyseal tissue was first boiled. The magnitude of the angiogenic response to anterior pituitary glands increased with the age of the donor (from a minimum 15 days of embryonic development to a maximum between 2 and 6 weeks old). In view of the similarity of the profile of the angiogenic response and the reported changes in GH secretion, the angiogenic activity of GH was then examined. Considerable angiogenic responses were observed with GH; there being increases (P < 0.05) in number of new blood vessels on the CAM of chick embryos on which native chicken GH or native bovine GH or recombinant bovine GH were added. These data support GH having an angiogenic action.

Effect of growth hormone and thyroid hormone on autoimmune thyroiditis in obese chickens

The effect of thyroxine (T4) and recombinant (rcGH) or purified pituitary-derived (pcGH) chicken growth hormone on the development of spontaneous autoimmune thyroiditis (SAT) was examined in the Obese strain (OS) chicken. Day-old OS chicks were randomly assigned to a control or 1.0 ppm T4 supplemented diet and a vehicle or 500 micrograms rcGH/kg BW daily injection, using a 2 x 2 factorial design. At 4 weeks, sera were analyzed for anti-thyroglobulin autoantibody (TgAAb) using a kinetics-based ELISA. Leucocytic infiltration of the thyroid was assessed using computer-based video imaging techniques. A close correlation between TgAAb and thyroid infiltration was seen with both being decreased (p < 0.05) by the T4/rcGH treatment. Neither the T4 or rcGH alone produced this effect and the rcGH treatment significantly elevated TgAAb. In a second experiment, all but the control group received 1.0 ppm T4 supplementation and two of the T4-treated groups received either 50 or 200 micrograms pcGH/kg BW by daily injection. As before, T4/pcGH significantly reduced TgAAb and thyroid infiltration. T4 alone produced no significant effects. These data support the conclusion that the combined treatment of T4 and cGH exert an immunomodulatory effect within a strain that is predisposed to autoimmune thyroiditis while GH treatment alone exacerbated the condition. These results also show that video imaging techniques can be used to evaluate the extent of histopathology present within the OS thyroid.

Study on the purification of growth hormone-like substance from pituitaries of the snake Ptyas mucosa

Extract from the snake (Ptyas mucosa) pituitaries was capable of inhibiting the binding of 125I-labelled bovine growth hormone to female rat liver membranes. The growth hormone-like substance was not adsorbed on Concanavalin A-Sepharose nor DEAE-cellulose, but could be purified by gel filtration on Sephadex G-50. It possessed a molecular weight of about 19,000 as judged by SDS-polyacrylamide gel electrophoresis. The iodinated snake growth hormone-like substance bound to membranes prepared from female rat and pregnant rabbit livers. The binding could be inhibited by unlabelled snake growth hormone-like substance as well as by bovine growth hormone.

Immunocytochemical studies of chicken somatotrophs and somatotroph granules before and after hatching

Immunocytochemical methods were used to gain information about the embryonic development of chicken somatotrophs before and after hatching. To localize growth hormone, anterior pituitary sections were incubated with growth-hormone antibody, and then an indirect peroxidase method was used for light microscopy and an immunogold method for electron microscopy. The earliest evidence of embryonic somatotrophs was seen at 12 days. At this stage somatotrophs were sparse (0.2% of parenchymal cells) and their granules were pleomorphic with elongated ovoid and lozenge shapes predominating. Few of the immunogold-labeled somatotroph granules of the embryo were spherical until 15 days after fertilization. At 18 days, most of the granules were spherical (their shape in the adult chicken). During the six days between the 15-day-old embryo and the 1-day-old chick, the number of gold particles per granule section approximately doubled suggesting an increase in growth hormone content of the granules. This rise was the result of increases in the size of the granule sections and in the concentration of gold particles in the sections. During the embryonic period of 12-20 days, somatotrophs were not more than 3.6% of the anterior pituitary cell population. During the following two days, between the 20-day-old embryo and the 1-day-old chick, the percentage of somatotrophs in the pituitary parenchymal cell population rose rapidly from 3.6% to 20.7% and then increased slowly to 24.6% during the period of 1-5 days after hatching.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of androgen (testosterone, 5 alpha-dihydrotestosterone, 19-nortestosterone) administration on growth in turkeys

The present studies examined the effect of three androgens, testosterone, a reduced form 5 alpha-dihydrotestosterone (5 alpha-DHT), and the readily aromatizable anabolic androgen, 19-nortestosterone, on growth in male and female turkeys. Growth (body weight, average daily gain, and right breast muscle weight) was increased by testosterone (females), 5 alpha-DHT (males and females), and 19-nortestosterone (males and females). Moreover, both feed:gain ratio and the weight of abdominal adipose tissue was reduced in turkeys treated with testosterone (females), 5 alpha-DHT (males and females), and 19-nortestosterone (females and males). Bursa of Fabricius weights were reduced in androgen-treated male or female turkeys with the decrease following 19-nortestosterone being greater than those observed with either testosterone or 5 alpha-DHT. Androgen treatment had no effect on skeletal growth (as indicated by shank-toe length) or weights of the liver, spleen, or testes. In female turkeys, plasma concentrations of hormones were determined following androgen treatment. No effects were observed on plasma concentrations of insulin-like growth factor-I or luteinizing hormone after any androgen treatment. Testosterone administration was followed by a physiological increase in the plasma concentrations of testosterone. Plasma concentrations of growth hormone were unaffected by either 5 alpha-DHT or 19-nortestosterone but reduced by the high dose of testosterone. The effect of castration on growth in the presence or absence of 19-nortestosterone was also examined. Castration did not depress growth compared with sham-operated controls, but increased adiposity. 19-Nortestosterone increased growth of castrated turkeys, increased muscle weight, and reduced abdominal adipose tissue weight.

Triiodothyronine (T3) inhibition of growth hormone secretion by chicken pituitary cells in vitro

These studies examined the cellular basis for the inhibitory effects of triiodothyronine (T3) on growth hormone-releasing factor (GRF)-evoked growth hormone (GH) release from chicken anterior pituitary cells in vitro. A primary monolayer culture of anterior pituitaries from 4- to 8-week-old White Leghorn cockerels was performed as previously described by this laboratory. Following a 72-hr preincubation period, cells were washed and incubated (2 hr) with either secretagogues or media alone (control). T3 (20 ng/ml) or vehicle was added to cells during both the preincubation (48-72 hr) and incubation (2 hr period. Triiodothyronine reduced (P less than 0.05) GH release (ng/ml) in response to (1) GRF; (2) the adenylyl cyclase stimulator, forskolin; (3) the cAMP analog and protein kinase A activator, 8-bromo cAMP; and (4) the phorbol ester and protein kinase C activator, phorbol 12-myristate 13-acetate. Triiodothyronine reduced (P less than 0.05) the intracellular content of GH and total GH (released GH and intracellular GH) irrespectively of whether secretagogues were also present. When GH release was expressed as a percentage of total GH [released GH/(intracellular GH + released GH)], percentage GH released in response to GRF, or the protein kinase A, protein kinase C, or calcium pathway activators was not as great in T3-treated versus non-T3-treated cells. These data indicate that T3 inhibits GRF-evoked GH release by reducing the availability of intracellular stores of GH and by also inhibiting second messenger-stimulated GH release pathways.

Possible involvement of adenylyl cyclase-cAMP-protein kinase a pathway in somatostatin inhibition of growth hormone release from chicken pituitary cells

Somatostatin (SRIF) reduces growth hormone releasing hormone (GRF)-stimulated growth hormone (GH) release from avian and mammalian adenohypophyseal cells. The present studies examined the intracellular mechanisms mediating SRIF inhibition of GRF-stimulated GH release from chicken pituitary cells. Increases (P less than 0.05) in GH release were observed in the presence of (1) GRF; (2) the adenylyl cyclase stimulator, forskolin; (3) a cAMP analog, 8-bromo-cAMP; (4) the phosphodiesterase inhibitor 3-isobutyl-l-methyl-xanthine (IBMX) combined with GRF; (5) a tumor-promoting phorbol ester and protein kinase C activator, phorbol 12-myristate, 13-acetate (PMA); (6) a diacylglycerol analog, 1,2-dioctanoyl-glycerol (DiC8); and (7) a calcium ionophore, A23187, alone and in combination with PMA. Somatostatin (10 ng/ml) reduced the release of GH stimulated by GRF, forskolin, and 8-bromo cAMP and the GRF-provoked release of GH in the presence of IBMX (P less than 0.05). Somatostatin, however, did not influence GH release in the presence of the protein kinase C activators, PMA or DiC8, or the calcium ionophore A23187. These data suggest that SRIF inhibits GRF-provoked GH release by reducing the ability of the cAMP-protein kinase A but not of the calcium or protein kinase C intracellular message pathways to stimulate GH release.

Central somatostatinergic regulation of growth hormone secretion in dwarf chickens

1. Basal circulating growth hormone (GH) concentrations in sex-linked-dwarf (SLD) chickens were unaffected by the intracerebroventricular (icv) injection of 10, 50 or 100 micrograms somatostatin (SRIF). 2. The GH response to systemic thyrotropin-releasing hormone (TRH; 10 micrograms/kg, iv) was, however, 'paradoxically' enhanced 20 min after icv SRIF administration. 3. A lower dose (1.0 micrograms) of SRIF had no effect on basal or TRH-induced GH release. 4. High-titre SRIF antisera (4 microliters) also had no acute effect on basal plasma GH concentrations, but augmented the GH response to TRH challenge. 5. SRIF would appear to act at central sites to modulate stimulated GH secretion in SLD chickens.

Stimulation of chicken growth hormone release by phorbol esters

Synergism between thyrotropin-releasing hormone (TRH) and human pancreatic growth hormone-releasing factor (hpGRF) has been shown in a primary (48 hr) culture of chicken adenohypophyseal cells established in this laboratory. The purpose of the present study was to determine if phorbol esters acting alone or in concert with TRH or hpGRF affect chicken GH release. Collagenase-dissociated chicken adenohypophyseal cells were treated (2 hr) with combinations of TRH, hpGRF, phorbol esters (activators of protein kinase C; PKC), and pharmacologic agents that increase cAMP. Phorbol myristate acetate (PMA) or phorbol dibutyrate (PDBu) alone stimulated GH release in a dose-dependent manner; either phorbol ester (10(-6) M) increased GH release from 100 to 390% over the value obtained in the absence of test agents (control). Similarly, hpGRF (10(-9) M), 8 Br-cAMP (10(-3) M), forskolin (10(-6) M), or isobutylmethylxanthine (IBMX, 10(-3) M) alone elevated GH release by at least 60% over the control value. The combined effects of phorbol esters (either PMA or PDBu) and hpGRF, 8 Br-cAMP, or forskolin on GH release were additive. Only one combination, phorbol esters with IBMX, exerted synergistic effects on GH release. No synergy was shown between TRH (1.3 x 10(-9) M) and either phorbol ester. These findings are the first to implicate PKC in chicken GH release in vitro. In addition, these studies, together with previous results, suggest that TRH and hpGRF synergy occurs via a pathway that arises prior to activation of PKC.

Influence of androgens on plasma concentrations of growth hormone in growing castrated and intact chickens

Castrated chicks implanted with testosterone or 5 alpha-dihydrotestosterone (5 alpha-DHT) had circulating concentrations of the respective androgen similar to or less than in sham-operated chicks. In castrated chicks, 5 alpha-DHT or 19-nortestosterone (19-NorT) inhibited growth as indicated by body weight, while testosterone and 5 beta-dihydrotestosterone (5 beta-DHT) were without effect. In intact male or female chicks, growth was inhibited by either testosterone or 5 alpha-DHT but was unaffected by 5 beta-DHT or estradiol-17 beta. Plasma concentrations of luteinizing hormone (LH) were reduced in castrated chicks receiving implants of either testosterone or 19-NorT. Only the highest dose of 5 alpha-DHT depressed the circulating concentration of LH; lower doses of 5 alpha-DHT being without effect. During the first 6 weeks of growth, plasma concentrations of GH were unaffected by most steroid treatments (5 alpha-DHT, 5 beta-DHT, low doses of testosterone, estradiol-17 beta) in castrated or in intact male or in female chicks. Similarly, 19-NorT did not affect plasma concentrations of GH in castrated chicks. The high dose of testosterone, however, depressed plasma concentrations of GH in castrated chicks between 2 and 6 weeks of age. Between 8 and 12 weeks of age, all steroids tested, except 5 alpha-DHT, were without effect on plasma concentrations of GH. Plasma concentrations of GH were increased in 5 alpha-DHT-treated chickens. This effect was observed irrespective of dose of 5 alpha-DHT or whether the androgen was administered to castrated or to intact male or to female chicks.

Influence of catecholamines, prostaglandins and thyroid hormones on growth hormone secretion by chicken pituitary cells in vitro

In young chickens plasma concentrations of growth hormone (GH) are depressed by prostaglandins (PG) E1 and E2, epinephrine, norepinephrine, alpha 2 and beta agonists or thyroid hormones. A primary culture of chicken adenohypophyseal cells was used to examine the direct effects of these agents at the level of the pituitary as evaluated by GH release in the presence and absence of growth hormone releasing factor (GRF). Following collagenase dispersion and culture (preincubation, 48 hr) cells were exposed (incubation, 2 hr) to test agents, except for thyroid hormones which were added during the preincubation, and incubation period. Growth hormone release was increased (P less than .05) in the presence of PGE1 (10(-8)M by 34%; 10(-7)M by 54%), PGE2 (10(-8)M by 29%; 10(-7)M by 29%), PGF2 alpha (10(-8)M by 28%), and the beta agonist isoproterenol (10(-7)M by 46%). Basal GH release from chicken pituitary cells was not affected by dopamine, norepinephrine, epinephrine, thyroxine (T4), triiodothyronine (T3), or alpha adrenergic agonists. Growth hormone releasing factor stimulated GH release was not affected by the presence of prostaglandins E1, E2 or F2 alpha in the incubation media. However, GRF stimulated GH release was reduced by high doses of catecholamines: dopamine (10(-6)M by 34%), norepinephrine (10(-6)M by 74%), epinephrine (10(-8)M by 47%; 10(-7)M by 41%; 10(-6)M by 89%), and by the alpha 1 adrenergic agonist, phenylephrine (10(-7)M by 52%), the alpha 2 agonist, clonidine (10(-8)M by 34%; 10(-7)M by 83%) and the beta agonist, isoproterenol (10(-7)M by 64%).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of estrogen on calcium homeostasis and pituitary hormones in the growing chick

An experiment was carried out to investigate the effect of a range of estradiol (E2) doses (0.1-6.5 micrograms/g body wt/day) on vitamin D metabolism and the plasma levels of growth hormone (GH) and prolactin (PRL) in the growing chick. Doses of 0.5-0.7 microgram/g E2, which are insufficient to raise the plasma calcium level, did induce an increase in growth rate, an increase in 25-hydroxyvitamin D 1 alpha-hydroxylase (1-hydroxylase) and 24-hydroxylase activities, and an increase in plasma GH level. These parameters leveled off or fell over the dose range 1-2 micrograms/g E2 but there was evidence of a second peak in 1-hydroxylase activity at 6 micrograms/g E2. At this high dose rate, the plasma Ca level rose to 8 mM, as it does in the laying hen; 24-hydroxylase activity, growth rate, and plasma GH and plasma PRL levels all decreased. It was concluded that the dose response to estrogen in the growing chick is not linear and, in the case of 1-hydroxylase activity, may even be biphasic.

Partial biochemical and biological characterization of purified chicken growth hormone (cGH). Isolation of cGH charge variants and evidence that cGH is phosphorylated

Chicken growth hormone (cGH) was purified from frozen pituitary glands obtained from recently sacrificed broilers. Glands were homogenized in a protease inhibitor solution (0.5 mM PMSF, 50 KIU/ml aprotinin, pH 7.2); extract was taken to pH 9.0 with calcium hydroxide and the supernatant was differentially precipitated with 20% (fraction A) and 50% (fraction B) ammonium sulfate. cGH (fraction B-DE-1) was obtained in pure form from fraction B after DEAE-cellulose chromatography at pH 8.6, with a yield of 2.9 mg/g tissue. Three charge variants of cGH (Rf = 0.23, 0.30, and 0.35) could be isolated by electroelution after semipreparative nondenaturing polyacrylamide gel electrophoresis of fraction B-DE-1. These charge variants showed the same apparent molecular weight (26,300 Da) by sodium dodecyl sulfate polyacrylamide gel electrophoresis under reducing conditions. Isoelectric focusing of fraction B-DE-1 revealed two major components (pI = 7.2 and 7.4) and four minor bands (pI = 6.2, 6.7, 7.1, and 7.5). It was found that fraction B-DE-1 contained a significant amount of esterified phosphate (1 nmol PO4/3.5 nmol protein) similar to that reported previously for ovine GH. The functional integrity of the cGH obtained here was characterized by two heterologous and one homologous bioassays. High activity was shown by fraction B-DE-1 in the tibia assay (1.76 UI/mg) and in the liver ornithine decarboxylase assay (sixfold over control), both made in hypophysectomized rats; and it also stimulated lipolysis (138 and 215% at 10 and 100 ng/ml, respectively) on chicken abdominal adipose tissue explants.

Avian growth hormone receptor assay: use of chicken and turkey liver membranes

A sensitive avian growth hormone (GH) radioreceptor assay (RRA) was developed using recombinant chicken growth hormone (rcGH) and a membrane receptor preparation of chicken or turkey livers. The specific binding of 125I-labeled rcGH to a 47,800 X g pellet was 33-36% in a 16-20 h incubation period at 4 degrees C. Binding was time, temperature and pH dependent. Scatchard analysis indicated a single class of high affinity GH binding sites in chicken and turkey livers, with binding affinities of 1.03 X 10(10) liter/M and 1.11 X 10(10) liter/M, respectively, and corresponding binding capacities of 10.7 fmol and 21 fmol per mg protein. The sensitivity of the assay was 0.41 ng of rcGH. Intra- and inter-assay coefficients of variation were 5.3% and 9.7%, respectively. Bovine GH, ovine GH, and porcine GH competed effectively for the GH binding sites in chicken and turkey livers. Turkey prolactin (PRL) and porcine PRL showed little cross-reaction (less than 0.07%), while cross-reaction of ovine and bovine PRL was greater (less than 10%). Standard rcGH (0.5-30 ng) was added to sera from hypophysectomized chickens and turkeys (hypox sera) and to tissue culture medium and was measured quantitatively. Untreated medium (10-100 microliters) and hypox sera (5-40 microliters) did not inhibit rcGH binding. These studies report the existence of specific binding sites for avian GH in chicken and turkey liver and validate a sensitive RRA for measurement of bioactive GH in sera and tissue culture medium.

Possible participation of calcium in growth hormone release and in thyrotropin-releasing hormone and human pancreatic growth hormone-releasing factor synergy in a primary culture of chicken pituitary cells

We previously reported that thyrotropin-releasing hormone (TRH) and human pancreatic growth hormone-releasing factor (hpGRF) exert synergistic (greater than additive) effects on growth hormone (GH) release from chicken pituitary cells in primary culture. In the present studies the possible participation of calcium in GH release and in TRH and hpGRF synergy was investigated. Following dispersion with collagenase, cells were cultured for 48 hr prior to exposure (2 hr) to test agents. Cultured cells were exposed to a range of calcium concentrations (0, 0.02, 0.2, and 2.0 mM) in the presence and absence of secretagogues. These results demonstrated that basal GH release was not altered by the concentration of calcium in the medium: however, secretagogue-induced GH release required calcium. Thus, TRH, hpGRF, 8 Br-cAMP, or forskolin stimulated GH release in the absence of calcium. Furthermore, synergistic GH release evoked by TRH and hpGRF, 8 Br-cAMP, or forskolin was observed only at the highest calcium concentration (2.0 mM). In other studies, ionomycin (10(-5) M), a calcium ionophore, stimulated GH release to a value about 125% over the basal (absence of test agent) value. Ionomycin-induced GH release was not affected by TRH (5.0 ng/ml); the combined effects of ionomycin (10(-7)-10(-5) M) and hpGRF (5.0 ng/ml) on GH release were less than additive. However, ionomycin (10(-5) M) further increased GH release over that resulting from the synergistic action of TRH and hpGRF (5.0 ng/ml each). Verapamil (a calcium channel blocker) did not affect GH release induced by either TRH or hpGRF (5.0 ng/ml each). However, this agent did inhibit synergistic GH release evoked by TRH and hpGRF, 8 Br-cAMP, forskolin, or isobutylmethylxanthine. These results suggest that calcium participates in secretagogue-induced GH release from chicken somatotrophs in vitro.

Relationships among mineral balance in the diet, early growth manipulation, and incidence of tibial dyschondroplasia in different strains of meat type chickens

In two experiments, a high dietary level of available phosphorus (.65%) in the presence of high chloride concentrations (.36%) was associated with a significant increase in the incidence of tibial dyschondroplasia (TD) in male broiler chickens. The level of dietary calcium and the interaction between Ca and available P had no effect on TD. Heterozygous normal (DW/DW) male broilers had a significantly lower incidence of TD than homozygous normal (Dw/Dw) chicks (Experiments 1 and 2). In Experiments 3 and 4, there were no significant differences between BW at 14 days for roaster-broiler cross and broiler chicks. At 21 and 28 days, however, the roaster-broiler cross chicks weighed significantly less than the broilers and had a significantly lower incidence of TD. Decreasing growth rates in broiler chicks after 14 days of age resulted in a significant decrease in the incidence of TD (Experiments 4 and 5), but did not decrease the severity of TD lesions at 28 days (Experiment 5). Depressed growth from 0 to 14 days decreased, but did not eliminate, TD lesions (45%) at 28 days, but it did significantly decrease the severity of the lesions compared with that in the 14 to 28-day manipulation treatments (Experiment 5). In Experiment 5, chicks were growth restricted from 0 to 14 or 14 to 21 days and then ad libitum fed the control diet until 28 days of age. The serum growth hormone concentrations at 28 days were inversely related to the rate of BW gain from 21 to 28 days of age, independent of BW at 21 or 28 days or feed consumption from 21 to 28 days. There were no differences in serum concentration of thyroxine or triiodothyronine at 28 days.

Somatostatin inhibition of thyrotropin-releasing hormone- and growth hormone-releasing factor-induced growth hormone secretion in young and adult anesthetized chickens

The present communication examines the influence of somatostatin (SRIF14) on basal and thyrotropin-releasing hormone (TRH)- or growth hormone-releasing factor (GRF)-induced GH secretion in young (6 week old) and adult male chickens. Studies were performed in sodium pentobarbitone-anesthetized chickens where basal plasma concentrations of GH are low and both TRH and GRF consistently stimulate GH release. In both young and adult chickens, basal GH secretion was reduced by SRIF14 infusion (3 micrograms/kg/min). Similarly, in adult and young birds, the GH secretory response to a challenge with a GRF bolus (10 micrograms/kg) was inhibited by the concomitant intravenous infusion of SRIF14 (0.3 or 3.0 micrograms/kg/min). In adult chickens, the GH response to TRH (10 micrograms/kg) was suppressed (by 93%) by SRIF14 infusion (3 micrograms/kg/min) and tended to be inhibited (by 29%) by a lower dose of SRIF14 (0.3 micrograms/kg/min). In contrast, in young chicks, GH release following TRH challenge (either 1 or 10 micrograms/kg) was only partially inhibited by SRIF14 infusion (3 micrograms/kg/min). The response to a TRH challenge (10 micrograms/kg) was unaffected by the low dosage of SRIF14 infusion (0.3 micrograms/kg/min). It is concluded that SRIF14 inhibits both GRF- and TRH-stimulated GH release in young and adult chickens.

Influence of beta-agonist on plasma concentrations of growth hormone in broiler chickens on a low plane of nutrition

The effect of the chronic administration of a beta-agonist (L-640,033; donated by Merck, Sharp and Dohme, Research Laboratories, Rahway, NJ) on both the plasma concentration of growth hormone (GH) and the episodic pattern of GH secretion was examined. Administration of .25, 1.0, or 4.0 ppm beta-agonist in the diet for only 3 to 5 days did not affect the overall mean plasma concentration of GH. These treatments also did not influence the frequency of GH secretory pulses. However, the amplitude of the GH secretory pulses was reduced. In contrast, administration of 1.0 ppm beta-agonist for the 10 to 12-day period increased the mean plasma concentration of GH, the amplitude of the GH secretory pulses, the basal (between pulses) plasma concentration of GH, and the interpeak interval. No effect of in vivo GH secretion was found with .25 ppm beta-agonist treatment for 10 to 12 days. Chicks receiving 4.0 ppm beta-agonist for 10 to 12 days had GH secretory pulses with increased amplitude, but no other differences in GH secretory characteristics were observed.

Hormonal correlates of migration and territorial behavior in juvenile willow tits during autumn

This study compared plasma levels of dihydrotestosterone, testosterone, corticosterone, luteinizing hormone, growth hormone, and prolactin in migrating juvenile willow tits with those in territorial juveniles. Both categories of birds were caught in late September. Migrating juveniles had higher plasma levels of corticosterone than territorial juveniles. Only corticosterone secretion was affected by "handling stress" in both migrating and territorial juveniles. However, territorial birds showed a much stronger relationship between these two variables. It is suggested that high corticosterone levels are involved in the emigration of juveniles out of the coniferous forest. Only juveniles were found among the migrating willow tits, and these birds were not well adapted for migration. Migrating juvenile males had less fat stored than did territorial ones. Furthermore, migrating juvenile males had higher liver/somatic index and higher plasma levels of growth hormone than did territorial males. These results indicate that migrating males had been, or were, exposed to food restrictions. The same proportion of migrating and territorial juveniles, males as well as females, had high plasma levels of testosterone. We suggest that these high levels were caused by recent aggressive interactions. To test the hypothesis that high plasma levels of testosterone are important for a juvenile to become a member of a territorial winter group, we performed a field experiment in which juveniles were given testosterone implants (controls were given empty silastic tubes) at the beginning of the territorial establishment period. The same proportion of testosterone-implanted birds and control birds succeeded in becoming members of territorial winter groups. Thus, testosterone does not seem to play an essential role in autumn territoriality, and it does not prevent autumn migration.

Growth hormone and somatostatin in the plasma of transiently diabetic ducks: basal variation and response to glucose

In the duck, subtotal pancreatectomy induces a transient diabetes, with decreased insulin and glucagon basal levels as well as responses to glucose. At the same time, a transient increase in basal peripheral somatostatin occurs, followed by an increase in growth hormone in the postdiabetic state. Intravenous glucose induces a slight decrease in somatostatin secretion in normal, but not in diabetic animals, and no significant variation in growth hormone secretion at any state. An obvious role of growth hormone or somatostatin in the development of this transient diabetes in the duck could not be detected in this study.

Seasonal changes in body weight, fat depots, and plasma levels of thyroxine and growth hormone in free-living great tits (Parus major) and willow tits (P. montanus)

Annual changes in body weight, fat depots, and plasma levels of thyroxine (T4) and growth hormone (GH) were studied in free-living great tits and willow tits. Birds were collected during six ecologically well-defined periods of the year. Special attention was given to the nonreproductive part of the year. T4 showed simple unimodal cycles in both species and both sexes, with high levels during the warmer part of the year, and low levels during the winter and spring periods. Although increasing levels were temporarily separated between the two species, they were in both cases correlated with the onset of gonadal regression and moult. Plasma levels of GH fluctuated in a much more complex pattern, and no obvious and consistent correlation to any extrinsic or intrinsic factor was found. Body weights and fat depots both showed seasonal variations that varied slightly between the two species. Values, with the exception for breeding females, were generally the highest during the autumn, winter, and spring periods.

Purification and characterization of bullfrog growth hormone

A highly purified growth hormone (GH) was isolated from an unadsorbed fraction obtained by subjecting acid acetone extract of bullfrog pituitary glands to DEAE-cellulose column chromatography, a side fraction obtained during the purification of prolactin, by cation-exchange chromatography on CM-Toyopearl and high-performance liquid chromatography on ODS with a yield of 5.6 mg/g protein of the starting material. Intraperitoneal injections of GH to hypophysectomized Xenopus resulted in a considerable elevation of chondroitin sulfate synthesis in the xiphisternal cartilage as measured in vitro. The bullfrog GH had a molecular weight of 22,000 Da as determined by sodium dodecyl sulfate-gel electrophoresis. The isoelectric point of bullfrog GH was estimated to be 7.8 by gel electrofocusing. The partial amino acid sequences of bullfrog GH at both terminal regions were determined.

Triiodothyronine inhibition of thyrotropin-releasing hormone- and growth hormone-releasing factor-induced growth hormone secretion in anesthetized chickens

The ability of triiodothyronine (T3) to reduce basal and secretagogue-induced growth hormone (GH) release was examined in anesthetized young and adult male chickens. Infusion of T3 had no effect on basal plasma concentrations of GH in either young or adult chickens. However, GH secretion following challenge with either thyrotropin-releasing hormone (TRH) or growth hormone-releasing hormone (GRF) was reduced, in a dose-dependent manner, by the infusion of T3. In vivo sensitivity to T3 inhibition was greater with TRH- than GRF-stimulated GH release in either young (ED50 for TRH-induced GH release, 0.34 microgram T3/kg/min; ED50 for GRF-induced GH release, 0.49 microgram T3/kg/min) or adult chickens (ED50 for TRH-induced GH release, 0.11 microgram T3/kg/min; ED50 for GRF-induced GH release 1.89, micrograms T3/kg/min). Moreover, there was an increase in sensitivity of TRH-induced GH release to T3 with age.

Growth hormone release from chicken anterior pituitary cells in primary culture: TRH and hpGRF synergy, protein synthesis, and cyclic adenosine 3'5'-monophosphate

Our earlier work showed that the effects of thyrotropin-releasing hormone (TRH) and human pancreatic growth hormone-releasing factor (hpGRF) on growth hormone (GH) release are synergistic (greater than additive) in a primary culture of chicken adenohypophyseal cells. The purpose of the present studies was to investigate the possible participation of protein synthesis and cyclic adenosine 3'5'-monophosphate (cAMP) in GH release. Following culture (48 hr), cells were incubated for 2 hr with test agents. Cycloheximide (an inhibitor of protein synthesis) had no effect on basal (absence of test agent) GH release or hpGRF-induced GH release. However, cycloheximide abolished the synergy between TRH and hpGRF. Although neither TRH nor hpGRF alone stimulated GH production (intracellular GH plus GH release) during a 2-hr incubation period, in combination these secretagogues increased total GH. These findings suggest that GH release from the chicken somatotroph under conditions of TRH and hpGRF synergy requires protein synthesis. In other studies, cells were exposed to agents inducing the formation of cAMP and either TRH or hpGRF. 8 Br-cAMP (10(-3) M), forskolin (10(-6) M), or isobutylmethylxanthine (IBMX; 10(-3) M) alone stimulated GH release to values between 30 and 50% over the basal value. The combined effects of each of these agents and TRH on GH release were synergistic. Similarly, IBMX and hpGRF exerted synergistic effects on GH release. In contrast, no synergy was shown between hpGRF and either 8 Br-cAMP or forskolin; their combined actions were less than additive.

Heterogeneity of chicken growth hormone (cGH). Identification of lipolytic and non-lipolytic variants

The identification and biological activity of chicken growth hormone (cGH) charge variants is described. On the basis of electrophoresis and immunoreactivity chicken pituitary glands contain at least two "charge" variants (Rf = 0.22 and 0.3) which have different net charge but similar molecular weight (26,300 d). Both are immunoreactive but show different bioactivity with adipose explants, band 0.22 being lipolytic whereas band 0.3 appears to be inactive. The abundance of these cGH bands vary with age, both being higher in young birds and lower in adults. These results suggest that cGH variants may have different biological actions.

Acute effects of hypophysectomy and administration of pancreatic and thyroid hormones on circulating concentrations of somatomedin-C in young chickens: relationship between growth hormone and somatomedin-C

The short-term control of plasma concentrations of somatomedin C (SmC) in young chicks was examined by either surgical removal of the pituitary gland or by the administration of hormones which affect plasma concentrations of growth hormone (GH). As expected, removal of the source of GH by hypophysectomy reduced plasma concentration of GH, these being suppressed by 95.7% within 1 hour. Hypophysectomy was rapidly followed by reductions in the plasma concentration of SmC. For instance, plasma concentrations of SmC were decreased to 53% of pretreatment one hour following hypophysectomy. This suggests both that SmC has a short half life and that the release of SmC into the circulation is tightly coupled to the presence of pituitary hormone(s), presumably including GH. Sham surgery also decreased plasma concentrations of GH but were without effect on plasma concentrations of SmC. The short term control of plasma concentrations of SmC was also examined by the acute administration of hormones, which affect GH secretion in vivo. Injections of thyroxine or triiodothyronine decreased the plasma concentration of GH but were without effect on the plasma concentration of SmC. On the other hand, the administration of either glucagon or insulin decreased the plasma concentration of both GH and SmC. The present data suggest that plasma concentrations of SmC do not simply reflect the GH status in young chickens.

The effect of low levels of dietary protein and calcium on growth rate, growth hormone, and vitamin D metabolism in the chick

Two experiments were carried out on 2-week-old chicks in which they were fed protein-deficient diets for varying lengths of time with or without calcium (Ca). All deficient diets depressed the rate of growth; this depression was more marked in chicks fed the protein-deficient diet for 21/2 days than in those fed the diet for 4 days. The circulating growth hormone level was high in all protein-deficient diets but low in the diet only deficient in calcium. The low Ca-induced-rise in renal vitamin D, 1-hydroxylase activity was reduced, and the plasma Ca level was particularly low, in chicks on the low protein/low Ca diet. The 24-hydroxylase activity was high on the low protein diets. It was concluded that adaptation to a low protein diet occurs over the first 4 days and that this may be associated with the high growth hormone level and also that adequate dietary protein is essential for maximal adaptation to dietary Ca deficiency.

Thyrotrophin-releasing hormone-induced growth hormone secretion in ducks: independence of peripheral plasma somatostatin, insulin, and glucagon

In young, but not old, ducks the iv infusion of thyrotrophin-releasing hormone (TRH) markedly increased peripheral plasma growth hormone (GH) concentrations, which remained elevated throughout the 30-min period of infusion. This GH response to TRH was suppressed by the simultaneous infusion of somatostatin, which increased the level of circulating somatostatin-like immunoreactivity (SLI) to supraphysiological levels. Basal concentrations of plasma SLI in both young and old birds were suppressed by TRH infusion. Concentrations of glucagon-like immunoreactivity (GLI) were increased by the infusion of TRH in young birds but not in adults, whereas plasma immunoreactive insulin (IRI) was decreased in young birds and increased in adults following TRH infusion. These results indicate that TRH-induced GH secretion in ducks is unrelated to changes in peripheral plasma SLI, GLI, or IRI induced by TRH infusion.