Endocrine modulation of physiological responses to catabolic disease

Disease or endotoxemia alters the plasma concentrations of anabolic hormones, particularly growth hormone (GH) and insulin-like growth-factor I (IGF-I). In general, these hormones are inhibited during the catabolic disease state. A hypothesis has evolved that anabolic hormones might be useful in patients’ recovery under these and other catabolic circumstances. The treatment of cattle with GH has provided significant improvement in the physiological response of the animals to the subsequent injection of bacterial lypopolysaccharide (LPS), perhaps via inhibition of tumor necrisis factor (TNF) release. However, this improved response to disease was not observed with animals treated with GH and infected with one of two parasitic organisms, Sarcocystis cruzi or Eimeria bovis. Recent attempts with other anabolic hormones, estradiol and progesterone, have proven remarkably effective in improving the adaptive physiological responses of calves to either E. bovis infection or to the injection of LPS. All animals displayed signs of infection, but the intensity and duration of symptoms were reduced. Although a mechanism is not yet known, there were no effects on TNF; cortisol; the percentages of lymphocytes expressing CD2, 4, or 8 antigens; or the production of antibodies.     

Modulation of the fish immune system by hormones

Immune-neuroendocrine interactions in fish, as in mammals, have become a focus of considerable interest, with the modulation of immune responses by hormones receiving particular attention. Cortisol, growth hormone (GH), prolactin (PRL), reproductive hormones, melanin-concentrating hormone (MCH) and proopiomelanocortin (POMC)-derived peptides have all been shown to influence immune functions in a number of fish species. This review summarises the known effects of these hormones on the fish immune system, as well as the often complex interactions between different hormones. The possible implications for fish health, with respect to aquaculture and the changes in immunocompetence that take place during different stages in the fish life cycle are also discussed.     

Environmental modulation of the immune system via the endocrine system

Numerous studies have demonstrated that a variety of hormones have receptors and exert biologic actions on tissues of the immune system. Conversely, cytokines exert biologic actions on the endocrine system. This bidirectional interaction is likely involved in maintenance of physiological and immunologic homeostasis. This paper summarizes a variety of actions of growth hormone (GH), prolactin (PRL), insulin-like growth factor-I (IGF-I), glucocorticoids and thyroid hormones (TH) on the immune system. It then proceeds to put these actions into a hypothetical context whereby these hormones may mediate some changes in immune system function in response to environmental stimuli such as physical and emotional stress, nutritional deprivation and environmental temperature. In the first example, it is proposed that PRL secretion in response to stress may serve an immunomodulatory role in two ways. The first is by stimulating the immune system directly and the second is by dampening or reducing the degree to which glucocorticoids are secreted in response to stress. The second example suggests that the increase in GH secretion and reduced IGF-I secretion in response to protein/energy restriction may have two potential immunomodulatory actions. One action is a direct effect of GH on several components of the immune system. The other is the partitioning of nutrient use away from skeletal muscle growth and toward tissues of higher priority such as the immune system. The third example proposes that the increased secretion of TH during cold environmental temperatures not only increases basic metabolic rate, but also directly stimulates both primary and secondary lymphoid tissues. It is suggested, therefore, that these three hormones are involved in maintaining immune system homeostasis in response to environmental change.     

Hormonal systems regulating growth. A reviewDès systèmes hormonaux maîtrisant la croissance. Une revue bibliographiqueWachstumsregulierende hormonsysteme. Eine literaturübersicht

Growth is a complex, highly integrated process. It involves a host of interactions between nutrients, environment, genotype, many very different hormones and the receptors for these hormones in different tissues. The ultimate hormones for growth are the growth hormone-dependent somatomedins. These are purely anabolic agents that stimulate increases in both the number of cells (hyperplasia) and their size (hypertrophy). Although the growth hormone-somatomedins axis is the central route for growth control, many other hormones influence their effectiveness. Growth hormone — despite being essential for somatomedin production — is also lipolytic and diabetogenic. It thus has both anabolic and catabolic actions. Insulin has some direct effects on hypertrophy, but also controls the ability of growth hormone to stimulate somatomedin production by regulating the growth hormone receptors involved in stimulating production of somatomedins. Similarly, thyroid hormones regulate somatomedin receptors. Just as insulin has direct and indirect anabolic actions, so glucocorticoids have catabolic actions of both a direct and indirect nature. Oestrogens also have direct and indirect effects, but these are antagonistic; on the one hand directly stimulating cell growth by hypertrophy and on the other inhibiting somatomedins production.Clearly there has to be a controlling mechanism which allows a change in the hormonal balance towards anabolism for growth to be stimulated. Identifying and altering this factor(s) will be the key to increasing growth by physiological hormonal manipulation. A major candidate for this role of central growth controller is somatostatin, which inhibits the release of growth hormone, insulin and thyroid hormones, and also acts as a regulator connecting nutrient entry and metabolism. Recent experiments which show that immunization against somatostatin increases growth and food conversion efficiency support this hypothesis.     

Role of the somatotropic axis in the mammalian metabolism

The metabolism in mammalian is regulated by multiple levels of hormone action, with complex feedback and control mechanisms. The somatotropic axis, essentially consisting of growth hormone (GH), insulin-like growth factors (IGF-I and -II), their associated carrier proteins, and receptors, plays a key role in the control of the regulation of metabolism and physiological process. Among this axis, other hormones like insulin, leptine, glucocorticoids or thyroid hormones are involved in this mechanism by modulating GH and/or IGF-I synthesis and availability. This review summarizes the complexity of the regulation of the metabolism by the somatotropic axis using different examples such as special nutritional situations or growth promoters administration.     

Central role of insulin in growth and development

Insulin has been shown to have an impact on both prenatal and postnatal growth. Specific mechanisms of insulin action on adipose cell function and lipid storage are well defined. Insulin probably acts in concert with other anabolic factors (i.e., growth hormone and somatomedins) to stimulate muscle protein anabolism and suppress protein catabolism (Figure 2). Insulin also plays a role in energy balance regulation by the hypothalamus, however exact mechanisms of effects on brain metabolism have not been clearly identified.     

Influence of cortisol,gonadal steroids and an energy deficit on biochemical indicators of bone turnover in Swine

In the pig a high growth potential seems to favour a disposition for skeletal problems. Hormones of growth hormone (GH)/insulin-like growth factor (IGF)-I axis as well as cortisol and gonadal steroids are endocrine determinants of the anabolic potential but their effects on bone turnover in pigs have not been described. Thus, key hormones were either infused for 7 days (cortisol, 5alpha-dihydrotestosterone (DHT), oestradiol) or influenced by Metyrapone (inhibition of cortisol synthesis) or energy deficit (increasing GH). Each treatment was carried out in six growing barrows/treatment. Bone turnover was characterized by daily measurements indirect parameter of osteoblastic and osteoclastic activity, osteocalcin (OC) and tartrate-resistant acid phosphatase (TRAP) respectively. All treatments except cortisol infusion seemed to favour bone formation, as they led either to a pronounced increase in OC (Metyrapone: +14%) or to significantly reduced TRAP (DHT: -9%, E2: -17%, energy deficit: -25%) followed by significantly higher OC (DHT: +9%, E2: +6%, energy deficit: +18%). Cortisol infusion affected bone loss mainly by a severe inhibition of osteoblastic activity (OC: -61%). Some reactions are explained by direct effects of the infused gonadal steroids on bone cells (inhibition of osteoclasts) or of the experimentally modified cortisol levels (inhibition of osteoblasts by cortisol). Other effects seem to be mediated by concomitant changes of IGF-I (inhibition of osteoclasts after energy deficit or cortisol) and GH-secretion (increased osteoblastic activity during energy deficit), respectively. Consequences for co-ordinated bone turnover are discussed.     

Prolactin: does it exert an up-modulation of the immune response in Trypanosoma cruzi-infected rats?

During the course of infection by Trypanosoma cruzi, the host immune system is involved in distinct, complex interactions with the endocrine system, and prolactin (PRL) is one of several hormones involved in immunoregulation. Although intensive studies attempting to understand the mechanisms that underlie Chagas' disease have been undertaken, there are still some pieces missing from this complex puzzle. Because data are scarce concerning the role of PRL involvement in Chagas' disease and taking into account the existence of crosstalk between neuroendocrine hormones and the immune system, the current study evaluates a possible up-regulation of the cellular immune response triggered by PRL in T. cruzi-infected rats and the role of PRL in reversing immunosuppression caused by the parasitic infection. The data shown herein demonstrate that PRL induces the proliferation of T lymphocytes, coupled with an activation of macrophages and the production of nitric oxide (NO), leading to a reduction in the number of blood trypomastigotes during the peak of parasitemia. During the acute phase of T. cruzi infection, an enhancement of both CD3+CD4+ and CD3+CD8+ T cell populations were observed in infected groups, with the highest numbers of these T cell subsets found in the infected group treated with PRL. Because NO is a signaling molecule involved in a number of cellular interactions with components of the immune system and the neuroendocrine system, PRL can be considered an alternative hormone able to up-regulate the host's immune system, consequently lowering the pathological effects of a T. cruzi infection.     

Protein metabolism in animals treated with anabolic agents

One of the major factors controlling the deposition of protein in an animal is the activity of the hormones circulating in its blood. Many of the anabolic hormones interact with each other e.g. growth hormone and insulin and there is evidence for a direct interaction between catabolic and anabolic hormones e.g. testosterone and glucocorticoids. Exogenously administered hormone-like substances can have marked effects on animal growth. Diethyl stilbestrol acts like an oestrogen elevating plasma insulin and growth hormone concentration. Zeranol probably also acts in a similar way.Trenbolone acetate (TBA) an androgenic agent, is a very effective growth promotor especially in ruminants. Few changes of note in the endogenous plasma hormone concentrations in treated ruminants have been reported although the combined implant of TBA plus 17-oestradiol did depress plasma thyroxine in steers. We have used the rat as a model to test the effects of TBA on protein synthesis and protein degradation rate in the muscle of rats. Protein synthesis and protein degradation in the muscle of treated female rats was shown to be markedly reduced, the increased growth rate being brought about by a greater reduction in the rate of degradation than in the rate of synthesis. Cathepsin D activity in the muscle was also reduced. Attempts to demonstrate a direct action of TBA on muscle have been unsuccessful. The currently favoured hypothesis for the mode of action of TBA is that it interferes with catabolic action of glucocorticoids on muscle protein. This may not be the mode of action of all androgenic agents. Durabolin (nandrolone phenyl propionate) would appear to stimulate both protein synthesis and protein degradation, at least in the rat.     

Biochemical proximates of pumpkin (Cucurbitaeae spp.) and their beneficial effects on the general well‐being of poultry species

There is a growing need to increase productivity in poultry. Growth hormones and antibiotics have the ability to improve health, weight gain and feed efficiency in meat‐producing animals. The growth‐promoting antibiotics are administered to poultry to improve the general performance of the chicken. However, the use of the xenobiotic drugs in food‐producing animals has been a concern and a sensitive issue of debate for several decades in the EU and many other regional blocks of the world. Consequently, the use of hormones in animal production has been banned in Italy, Denmark and Germany for over 4–5 decades, while Belgium and Greece had never permitted its use for livestock fattening purposes. Bioactive phytochemicals exhibit antimicrobial, antioxidant, antiparasitic, antiprotozoal, antifungal and anti‐inflammatory properties and consequently have several beneficial effects on appetite, growth and the immune status of the animal. In South Africa, different species of pumpkin are produced for food due to their high nutrient content. The flesh serves as a traditional food, while the seeds and peels are commonly discarded. Pumpkin seed extract is reported to be useful for immunomodulation, reproductive health, therapeutics over a wide range of disease conditions and stimulates metabolism of accumulated fats. Studies have also shown that pumpkin seeds are a valuable source of protein and fat. Their complexity and extent of bioactivity offers sustainable prospects for natural control of pathogenic/parasitic organisms, stimulate nutrition or enhance resistance to disease infections, and reduce abdominal fat and serum levels of harmful lipids, while increasing serum levels of beneficial lipids.     

The control of adenohypophysial hormone secretion by amino acids and peptides in swine

Several different amino acids and peptides control secretion of adenohypophysial hormones and this control may be indirect, via the modulation of hypothalamic hormone secretion. Indeed, classical hypothalamic hormones (e.g., gonadotropin-releasing hormone [GnRH], growth hormone-releasing hormone [GHRH], somatostatin, etc.) may be released into the hypothalamo-hypophysial portal vasculature, travel to the adenohypophysis and there stimulate or inhibit secretion of hormones. Alternatively, some amino acids and peptides exert direct stimulatory or inhibitory effects on the adenohypophysis, thereby impacting hormone secretion. In swine, the most extensively studied modulators of adenohypophysial hormone secretion are the excitatory amino acids (ExAA), namely glutamate and aspartate, and the endogenous opioid peptides (EOP). In general, excitatory amino acids stimulate release of luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), and prolactin (PRL). Secretion of adenohypophysial hormones induced by ExAA is primarily, but perhaps not exclusively, a consequence of action at the central nervous system. By acting primarily at the level of the central nervous system, EOP inhibit LH secretion, stimulate GH release and depending on the animal model studied, exert either stimulatory or inhibitory influences on PRL secretion. However, the EOP also inhibited LH release by direct action on the adenohypophysis. More recently, peptides such as neuropeptide-Y (NPY), orexin-B, ghrelin, galanin, and substance P have been evaluated for possible roles in controlling adenohypophysial hormone secretion in swine. For example, NPY, orexin-B, and ghrelin increased basal GH secretion and modulated the GH response to GHRH, at least in part, by direct action on the adenohypophysis. Secretion of LH was stimulated by orexin-B, galanin, and substance P from porcine pituitary cells in vitro. Because the ExAA and various peptides modulate secretion of adenohypophysial hormones, these compounds may play an important role in regulating swine growth and reproduction.     

Influence of nutritional deprivation on insulin-like growth factor I, somatotropin, and metabolic hormones in swine

Although growth hormone (GH) is a primary stimulus for the synthesis of insulin-like growth factor I (IGF-I), other factors such as nutritional status, insulin, and thyroid hormones are important modulators of circulating IGF-I levels. Thus, the effects of feed restriction and subsequent refeeding on plasma levels of IGF-I, GH, insulin, and thyroid hormones were studied in swine. Despite an elevation in plasma GH levels after 48 h of feed restriction, circulating IGF-I levels were decreased by 53% (P less than .05). Plasma triiodothyronine (T3) and insulin were lower (P less than .05) within 24 h after the feed restriction began, whereas thyroxine (T4) did not decrease until 48 h after removal of feed. Blood glucose levels remained unchanged throughout the experiment. Refeeding after the 48-h fast was associated with a decline (P less than .05) in circulating GH levels within 2 h, concomitant with an elevation (P less than .05) in plasma insulin and T3. Refeeding fasted pigs was associated with an increase (P less than .05) in plasma IGF-I; however, levels still had not returned to prefast concentrations within 24 h after refeeding. These data indicate that the GH-IGF-I axis becomes uncoupled during nutritional restriction in swine and that inadequate nutrient supply may limit the expression of the anabolic effects of GH.     

Technologies for the control of fat and lean deposition in livestock

When the ratio of lean to fat deposition is improved, so is feed conversion efficiency. Net benefits may include lower production costs, better product quality, less excretion of nitrogenous wastes into the environment, decreased grazing pressure on fragile landscapes, and reduced pressure on world feed supplies. However, finding a way to achieve these goals that is reliable, affordable, and acceptable to the majority of consumers has proved to be a major challenge. Since the European Union banned hormonal growth promoters (HGPs) 15 years ago, countries such as Australia and the United States have licensed new products for livestock production, including bovine growth hormone (GH), porcine and equine GH, and the beta-agonist ractopamine. There has also been considerable research into refining these products, as well as developing new technologies. Opportunities to improve beta-agonists include lessening their effects on meat toughness, reducing adverse effects on treated animals, and prolonging their duration of action. In the last regard, the combined use of a beta-agonist with GH, which upregulates beta-adrenoceptors, can produce an outstanding improvement in carcass composition and feed efficiency. Insulin-like growth factor-1 (IGF-1) mediates many of the actions of GH, but has proved to be of more use as a growth reporter/selection marker in pigs, than as a viable treatment. However, a niche for this product could exist in the manipulation of neonatal growth, causing a life-long change in lean:fat ratio. Another significant advance in endocrinology is the discovery of hormones secreted by muscle and fat cells, that regulate feed intake, energy metabolism, and body composition. Leptin, adiponectin and myostatin were discovered through the study of genetically obese, or double-muscled animals. Through genetic manipulation, there is potential to exploit these findings in a range of livestock species, although the production of transgenic animals is still hampered by the poor level of control over gene expression, and faces an uphill battle over consumer acceptance. There are several alternatives to HGPs and transgenics, that are more likely to gain world-wide acceptance. Genetic selection can be enhanced by using markers for polymorphic genes that control fat and lean, such as thyroglobulin, or the callipyge gene. Feed additives of natural origin, such as betaine, chromium and conjugated linoleic acid, can improve the fat:lean ratio under specific circumstances. Additionally, 'production vaccines' have been developed, which alter the neuro-endocrine system by causing an auto-immune response. Thus, antibodies have been used to neutralise growth-limiting factors, prolong the half-life of anabolic hormones, or activate hormone receptors directly. Unfortunately, none of these technologies is sufficiently well advanced yet to rival the use of exogenous HGPs in terms of efficacy and reliability. Therefore, further research is needed to find ways to control fat and lean deposition with due consideration of industry needs, animal welfare and consumer requirements.     

Determination of the temporal relationship between porcine growth hormone, serum IGF-1 and cortisol concentrations in pigs

We found previously that porcine growth hormone (pGH) causes an increase in growth rate with a concurrent improvement in carcass composition in pigs. The somatomedin, insulin-like growth factor 1 (IGF-1), is though to play a major role in mediating some of the anabolic actions of GH, while the glucocorticoid hormones are potential counter-regulators of these effects. The present study was conducted to determine the temporal and dose-response relationship between GH administration and serum IGF-1 and cortisol concentrations in pigs. Twelve Yorkshire barrows, fitted with femoral artery catheters, were injected (im) with either 0, 10, 100 or 1,000 micrograms/kg pGH. Blood sampling began 40 min prior to pGH injection and was continued for 37 h. Serum GH, IGF-1 and cortisol concentrations were determined by radioimmunoassay. In control animals, serum GH concentrations ranged from 1.6 to 5.7 ng/ml over 37 h. In the animals treated with increasing doses of pGH, peak serum GH concentrations reached 28, 112 and 286 ng/ml and levels remained elevated for 4, 12 and 24 h, respectively. Serum IGF-1 concentrations were elevated by pGH after a lag time of 4 to 6 h. When the IGF-1 concentrations were integrated over time, the response appeared to be dose-dependent, with an ED50 of 710 micrograms/kg body weight (BW). Data for serum cortisol concentrations showed a great deal of individual variation. A transient increase in cortisol was observed, but only in the group treated with 1,000 micrograms pGH/kg BW. Cortisol levels returned to baseline 2 h after pGH injection.(ABSTRACT TRUNCATED AT 250 WORDS)     

A proteomic analysis of the effect of growth hormone on mammary alveolar cell-T (MAC-T) cells in the presence of lactogenic hormones

The bovine mammary alveolar cell-T (MAC-T) cell line is able to uniformly differentiate and secrete casein proteins in response to dexamethasone, insulin, and prolactin and is extensively used to study bovine mammary epithelial cell (MEC) function. Somatotropin, or growth hormone (GH), has been shown to increase milk protein synthesis both in vivo and in mammary cell models and to induce cytoskeletal rearrangement in a 3T3 fibroblast cell line and a Chinese hamster ovary cell line. To identify the nature of the effects of GH in MECs cultured with lactogenic hormones, changes in global protein expression were assessed in the MAC-T cell line with the use of two-dimensional gel electrophoresis and matrix-assisted laser desorption ionization tandem time of flight mass spectrometry. Forty proteins were differentially expressed in response to GH (P < 0.05) and were related to metabolism, the cytoskeleton, protein folding, RNA and DNA processing, and oxidant stress. These widespread changes in protein expression are indicative of a global role of GH in overall cellular differentiation that may underlie the direct modulation of milk component synthesis in MEC models that have been described to date.     

Mammary growth hormone and tumorigenesis--lessons from the dog

The discovery in the early 1990s that progestin-induced growth hormone (GH) excess in the dog originates in the mammary gland can be seen as a hallmark in the research on the pathogenesis of mammary cancer in the dog. The local biosynthesis and release of GH may provide a highly proliferative environment in the mammary gland, which contributes to the development and/or progression of mammary tumours. Before final goals such as prevention of tumour formation or inhibition of tumour promotion can be achieved it is of eminent importance to elucidate the mechanism of progesterone-induced mammary GH production and the mechanism of local autocrine/paracrine action of GH. These local GH effects may be achieved through direct growth stimulating effects of GH as well as by indirect effects mediated by the stimulation of the biosynthesis of insulin-like growth factor-I (IGF-I). The biological effects of the IGFs largely depend on the presence of IGF binding proteins (IGFBPs) which may both enhance or inhibit the activity of the IGFs. This review concentrates on recent advances in the understanding of the local mammary GH-IGF axis and the lessons which can be drawn from the dog for mammary cancer research in other species.     

Regulation of the growth hormone and luteinizing hormone response to endotoxin in sheep

Infectious disease processes cause physiological adaptations in animals to reorder nutrient partitioning and other functions to support host survival. Endocrine, immune and nervous systems largely mediate this process. Using endotoxin injection as a model for catabolic disease processes (such as bacterial septicemia), we have focused our attention on regulation of growth hormone (GH) and luteinizing hormone (LH) secretion in sheep. Endotoxin produces an increase in plasma GH and a decrease in plasma LH concentrations. This pattern can be reproduced, in part, by administration of various cytokines. Antagonists to both interleukin-1 (IL-1) and tumor necrosis factor (TNF) given intravenously (IV) prevented the endotoxin-stimulated increase in GH. Since endotoxin will directly stimulate GH and LH release from cultured pituitary cells, the data suggest a pituitary site of action of the endotoxin to regulate GH. Studies with portal vein cannulated sheep indicated that gonadotropin releasing hormone was inhibited by endotoxin, suggesting a central site of action of endotoxin to regulate LH. However, other studies suggest that endotoxin may also regulate LH secretion at the pituitary. Thus, IL-1 and TNF regulate GH release from the pituitary gland while endotoxin induces a central inhibition of LH release.     

羊毛生长的内分泌调节研究进展

本文综述了GH、IGF、T3 、T4、PRL、褪黑激素、EGF、肾上腺皮质激素等激素对羊毛生长影响的研究进展 ,并对一些激素对羊毛生长的作用机制进行了分析。     

Comparative Aspects of the Endotoxin- and Cytokine-Induced Endocrine Cascade Influencing Neuroendocrine Control of Growth and Reproduction in Farm Animals

Disease in animals is a well-known inhibitor of growth and reproduction. Earlier studies were initiated to determine the effects of endotoxin on pituitary hormone secretion. These studies found that in sheep, growth hormone (GH) concentration was elevated, whereas insulin-like growth factor-I (IGF-I) was inhibited, as was luteinizing hormone (LH). Examination of the site of action of endotoxin in sheep determined that somatotropes expressed the endotoxin receptor (CD14) and that both endotoxin and interleukin-Iβ activated GH secretion directly from the pituitary. In the face of elevated GH, there is a reduction of IGF-I in all species examined. As GH cannot activate IGF-I release during disease, there appears to be a downregulation of GH signalling at the liver, perhaps related to altered nitration of Janus kinase (JAK). In contrast to GH downregulation, LH release is inhibited at the level of the hypothalamus. New insights have been gained in determining the mechanisms by which disease perturbs growth and reproduction, particularly with regard to nitration of critical control pathways, with this perhaps serving as a novel mechanism central to lipopolysaccharide suppression of all signalling pathways. This pathway-based analysis is critical to the developing novel strategies to reverse the detrimental effect of disease on animal production.     

The chicken pituitary-specific transcription factor PIT-1 is involved in the hypothalamic regulation of pituitary hormones

Pit-1 is a pituitary-specific POU-domain DNA binding factor, which binds to and trans-activates promoters of growth hormone- (GH), prolactin- (PRL) and thyroid stimulating hormone-beta- (TSHbeta) encoding genes. Thyrotropin-releasing hormone (TRH) is located in the hypothalamus and stimulates TSH, GH and PRL release from the pituitary gland. In the present study, we successfully used the cell aggregate culture system for chicken pituitary cells to study the effect of TRH administration on the ggPit-l* (chicken Pit-1), GH and TSHbeta mRNA expression in vitro. In pituitary cell aggregates of 11-day-old male broiler chicks the ggPit-l * mRNA expression was significantly increased following TRH administration, indicating that the stimulatory effects of TRH on several pituitary hormones are mediated via its effect on the ggPit-l* gene expression. Therefore, a semiquantitative RT-PCR method was used to detect possible changes in GH and TSHbeta mRNA levels. TRH affected both the GH and TSHbeta mRNA levels. The results of this in vitro study reveal that ggPit-1 * has a role in mediating the stimulatory effects of TRH on pituitary hormones like GH and TSHbeta in the chicken pituitary.