Pituitary Growth Hormone Secretion Research Articles

Estrogens Regulate the Hepatic Effects of Growth Hormone, a Hormonal Interplay with Multiple Fates

The liver responds to estrogens and growth hormone (GH) which are critical regulators of body growth, gender-related hepatic functions, and intermediate metabolism. The effects of estrogens on liver can be direct, through the direct actions of hepatic ER, or indirect, which include the crosstalk with endocrine, metabolic, and sex-differentiated functions of GH. Most previous studies have been focused on the influence of estrogens on pituitary GH secretion, which has a great impact on hepatic transcriptional regulation. However, there is strong evidence that estrogens can influence the GH-regulated endocrine and metabolic functions in the human liver by acting at the level of GHR-STAT5 signaling pathway. This crosstalk is relevant because the widespread exposition of estrogen or estrogen-related compounds in human. Therefore, GH or estrogen signaling deficiency as well as the influence of estrogens on GH biology can cause a dramatic impact in liver physiology during mammalian development and in adulthood. In this review, we will summarize the current status of the influence of estrogen on GH actions in liver. A better understanding of estrogen-GH interplay in liver will lead to improved therapy of children with growth disorders and of adults with GH deficiency.

Kalrnplays key roles within and outside of the nervous system

BackgroundThe human KALRN gene, which encodes a complex, multifunctional Rho GDP/GTP exchange factor, has been linked to cardiovascular disease, psychiatric disorders and neurodegeneration. Examination of existing Kalrn knockout mouse models has focused only on neuronal phenotypes. However, Kalirin was first identified through its interaction with an enzyme involved in the synthesis and secretion of multiple bioactive peptides, and studies in C.elegans revealed roles for its orthologue in neurosecretion.ResultsWe used a broad array of tests to evaluate the effects of ablating a single exon in the spectrin repeat region of Kalrn (KalSRKO/KO); transcripts encoding Kalrn isoforms containing only the second GEF domain can still be produced from the single remaining functional Kalrn promoter. As expected, KalSRKO/KO mice showed a decrease in anxiety-like behavior and a passive avoidance deficit. No changes were observed in prepulse inhibition of acoustic startle or tests of depression-like behavior. Growth rate, parturition and pituitary secretion of growth hormone and prolactin were deficient in the KalSRKO/KO mice. Based on the fact that a subset of Kalrn isoforms is expressed in mouse skeletal muscle and the observation that muscle function in C.elegans requires its Kalrn orthologue, KalSRKO/KO mice were evaluated in the rotarod and wire hang tests. KalSRKO/KO mice showed a profound decrease in neuromuscular function, with deficits apparent in KalSR+/KO mice; these deficits were not as marked when loss of Kalrn expression was restricted to the nervous system. Pre- and postsynaptic deficits in the neuromuscular junction were observed, along with alterations in sarcomere length.ConclusionsMany of the widespread and diverse deficits observed both within and outside of the nervous system when expression of Kalrn is eliminated may reflect its role in secretory granule function and its expression outside of the nervous system.

Kisspeptin-1 directly stimulates LH and GH secretion from goldfish pituitary cells in a Ca2+-dependent manner

It has been established that kisspeptin regulates reproduction via stimulation of hypothalamic gonadotropin-releasing hormone (GnRH) secretion, which then induces pituitary luteinizing hormone (LH) release. Kisspeptin also directly stimulates pituitary hormone release in some mammals. However, in goldfish, whether kisspeptin directly affects pituitary hormone release is controversial. In this study, synthetic goldfish kisspeptin-1(1–10) (gKiss1) enhances LH and growth hormone (GH) release from primary cultures of goldfish pituitary cells in column perifusion. gKiss1 stimulation of LH and GH secretion were still manifested in the presence of the two native goldfish GnRHs, salmon (s)GnRH (goldfish GnRH-3) and chicken (c)GnRH-II (goldfish GnRH-2), but were attenuated by two voltage-sensitive calcium channel blockers, verapamil and nifedipine. gKiss-induced increases in intracellular Ca2+ in Fura-2AM pre-loaded goldfish pars distalis cells were also inhibited by nifedipine. These results indicate that, in goldfish, (1) direct gKiss1 actions on pituitary LH and GH secretion exist, (2) these actions are independent of GnRH and (3) they involve Ca2+ signalling.

Associations of growth hormone secretagogue receptor (GHSR) genes polymorphisms and protein structure changes with carcass traits in sheep

Growth hormone secretagogue receptor (GHSR), a G protein-coupled receptor that binds ghrelin, plays an important role in the central regulation of pituitary growth hormone secretion, food intake, and energy homeostasis. Ghrelin receptor (GHSR) modulates many physiological effects and therefore is a candidate gene for sheep production performance. Polymorphism of the GHSR gene was detected by PCR–SSCP and DNA sequencing methods in 463 individuals. Two different structures in protein and nine single nucleotide polymorphisms (SNPs) were identified. The evaluation of the associations between these SSCP patterns with carcass traits suggests a positive effect of genotype TT and B structure on carcass weight, and body length (P<0.05). In addition, the animal with TC had greater abdominal fat than those with TT and CC (P<0.05) while CC genotype contributed to low blood cholesterol (P=0.04). The results confirm the hints suggesting that GHSR is a preferential target for further investigation on mutations that influence carcass trait variations.

Successful Treatment of Idiopathic Intracranial Hypertension (IIH) with Octreotide (P03.229)

Objective: To document a case of successful treatment of Ideopathic Intracranial Hypertension(IIH) with octreotide. Background Growth hormone mediated hyper secretion of CSF is the most accepted mechanism for IIH. Data from 57,968 children in the Pfizer International Growth Study database showed that IIH was one of the major side effects (80%) of GH. Octreotide, a somatostatin analogue, inhibits pituitary growth hormone(GH)secretion, and antagonizes GH and insulin like growth factor (IGF) action by blocking GH receptors. Design/Methods: A 39 year-old, obese female presented with headaches, intermittent visual blurring, and floaters for two years. Her examination was unremarkable except for papilloedema on fundoscopic exam. Computerized perimetry revealed marked impairment in the bilateral nasal fields. Brain MRI was normal, MR venogram showed hypoplastic left transverse venous sinus. The cerebrospinal fluid pressure was 30 cm of water, with a pulsatile CSF column. After initial use of diuretics being ineffective, lumbar punctures were recommended, but patient was not compliant to it. Results: Treatment with subcutaneous octreotide resulted in significant improvement of headaches, and normalization of visual fields and papilloedema. She tolerated the treatment well, except for formation of gallstones, for which treatment was stopped at around 9 months. However she continues to have persistent normalization of the vision and normal computerized perimetry after one and half year in follow up. Conclusions: Somatostatin receptors (SSTR I-5) are found in the choroid plexus, arachnoid granulations, and retina, which mediate the antisecretory and antiproliferative effects of somatostatin, which could be responsible for decreasing the intracranial pressure in IIH. Panagopoulos et al. treated 26 IIH patients with Octreotide for 6-8 months. Majority showed improvement of headache, visual symptoms, papilloedema and significant reduction of CSF pressure, which was persistent in follow up for three years. Further studies are warranted for its potential use in the treatment of IIH. Disclosure: Dr. Vyas has nothing to disclose. Dr. Phadke has received personal compensation for activities with Teva Neurosciences, Berlex and Glaxo Smith Kline as a speaker.

Orbital Metastasis of Pituitary Growth Hormone Secreting Carcinoma-Causing Lateral Gaze Palsy: Case Report, Pathology Review, and Review of the Literature

Orbital Metastasis of Pituitary Growth Hormone Secreting Carcinoma-Causing Lateral Gaze Palsy: Case Report, Pathology Review, and Review of the Literature

Antineoplastic Action of Growth Hormone-Releasing Hormone (GHRH) Antagonists

Some of the antagonists of growth hormone-releasing hormone (GHRH) are able to inhibit the growth of various experimental human cancers. The antitumor effects of first antagonists seemed to be dependent mainly on the disruption of pituitary secretion of growth hormone (GH), followed by the reduction in the levels of circulating insulin-like growth factor (IGF)-1, an important growth factor for cancer cells. It seems obvious, that growth hormone deficiency (GHD) induced by GHRH antagonists with all its complications, could limit the beneficial effects of GHRH antagonists therapy, and decrease patients' quality of life. The discovery of local autocrine/paracrine production of GHRH and other related growth factors in many tumoral tissues, in combination with the wide expression of GHRH receptors on cancer cells, directed the research to the synthesis of more potent GHRH antagonists. These compounds exert strong inhibitory effects directly on tumor growth, with scarce endocrine action. The receptor-mediated mechanisms comprise complex and still not completely understood effects on intracellular signaling pathways that are strictly related to human tumorigenesis. This review summarizes recent patents and latest observations on the antineoplastic role of GHRH antagonists in human tumors with emphasis on potential therapeutic applications in clinical oncology.

Growth hormone regulation of follicular growth

The somatotropic axis-consisting of growth hormone (GH), the insulin-like growth factors 1 and 2 (IGF1 and IGF2), GH binding protein (GHBP), IGF binding proteins (IGFBPs) 1 to 6, and the cell-surface receptors for GH and the IGFs-has major effects on growth, lactation and reproduction. The primary target tissues for GH are involved in growth and metabolism. The functionality of the somatotropic axis depends in part on the expression of liver GH receptor (GHR), which determines the amount of IGF1 released from the liver in response to GH. The IGF1 acts as a pleiotropic growth factor and also serves as the endocrine negative feedback signal controlling pituitary GH secretion. Growth hormone and IGF1 undergo dynamic changes throughout the life cycle, particularly when animals are either growing, early post partum or lactating. Cells within the reproductive tract can respond directly to GH but to a lesser degree than the primary target tissues. The major impact that GH has on reproduction, therefore, may be secondary to its systemic effects on metabolism (including insulin sensitivity) or secondary to the capacity for GH to control IGF1 secretion. Insulin-like growth factor 1 and IGFBP are also synthesised within the ovary and this local synthesis is a component of the collective IGF1 action on the follicle. Future studies of GH should focus on its direct effects on the follicle as well as its indirect effects mediated by shifts in nutrient metabolism, insulin sensitivity, IGF1 and IGFBP.

Calcium and other signalling pathways in neuroendocrine regulation of somatotroph functions

Relative to mammals, the neuroendocrine control of pituitary growth hormone (GH) secretion and synthesis in teleost fish involves numerous stimulatory and inhibitory regulators, many of which are delivered to the somatotrophs via direct innervation. Among teleosts, how multifactorial regulation of somatotroph functions are mediated at the level of post-receptor signalling is best characterized in goldfish. Supplemented with recent findings, this review focuses on the known intracellular signal transduction mechanisms mediating the ligand- and function-specific actions in multifactorial control of GH release and synthesis, as well as basal GH secretion, in goldfish somatotrophs. These include membrane voltage-sensitive ion channels, Na+/H+ antiport, Ca2+ signalling, multiple pharmacologically distinct intracellular Ca2+ stores, cAMP/PKA, PKC, nitric oxide, cGMP, MEK/ERK and PI3K. Signalling pathways mediating the major neuroendocrine regulators of mammalian somatotrophs, as well as those in other major teleost study model systems are also briefly highlighted. Interestingly, unlike mammals, spontaneous action potential firings are not observed in goldfish somatotrophs in culture. Furthermore, three goldfish brain somatostatin forms directly affect pituitary GH secretion via ligand-specific actions on membrane ion channels and intracellular Ca2+ levels, as well as exert isoform-specific action on basal and stimulated GH mRNA expression, suggesting the importance of somatostatins other than somatostatin-14.

Ghrelin potentiates TSH-induced expression of the thyroid tissue-specific genes thyroglobulin, thyroperoxidase and sodium-iodine symporter, in rat PC-Cl3 Cells

Ghrelin is a 28-amino-acid peptide that stimulates pituitary growth-hormone secretion and modulates food-intake and energy metabolism in mammals. It is mainly secreted by the stomach, but it is also expressed in many other tissues such as cartilage or the thyroid gland. In the present study we have analyzed by RT-PCR and using immunohistochemistry and immunofluorescence the expression and tissue distribution of ghrelin and its functional receptor (GHS-R type 1α) in thyroid cell-lines and in normal and pathological rat thyroid tissue. Additionally, by measuring the incorporation of BrdU, we have investigated if, as previously noted for FRTL-5 cells, ghrelin enhances the proliferation rate in the PC-Cl3 rat-thyrocyte cell-line. Finally, we have determined the stimulatory effect of ghrelin on TSH-induced expression of the tissue-specific key genes involved in the synthesis of thyroid hormone: thyroglobulin, thyroperoxidase and sodium–iodine symporter. Our data provide direct evidence that C-cell secreted ghrelin may be involved in the paracrine regulation of the thyroid follicular cell function.

Ghrelin and obestatin modulate growth hormone-releasing hormone release and synaptic inputs onto growth hormone-releasing hormone neurons

Ghrelin, a natural ligand of the growth hormone secretagogue receptor (GHS-R), is synthesized in the stomach but may also be expressed in lesser quantity in the hypothalamus where the GHS-R is located on growth hormone-releasing hormone (GHRH) neurons. Obestatin, a peptide derived from the same precursor as ghrelin, is able to antagonize the ghrelin-induced increase of growth hormone (GH) secretion in vivo but not from pituitary explants in vitro. Thus, the blockade of ghrelin-induced GH release by obestatin could be mediated at the hypothalamic level by the neuronal network that controls pituitary GH secretion. Ghrelin increased GHRH and decreased somatostatin (somatotropin-releasing inhibitory factor) release from hypothalamic explants, whereas obestatin only reduced the ghrelin-induced increase of GHRH release, thus indicating that the effect of ghrelin and obestatin is targeted to GHRH neurons. Patch-clamp recordings on mouse GHRH-enhanced green fluorescent protein neurons indicated that ghrelin and obestatin had no significant effects on glutamatergic synaptic transmission. Ghrelin decreased GABAergic synaptic transmission in 44% of the recorded neurons, an effect blocked in the presence of the GHS-R antagonist BIM28163, and stimulated the firing rate of 78% of GHRH neurons. Obestatin blocked the effects of ghrelin by acting on a receptor different from the GHS-R. These data suggest that: (i) ghrelin increases GHRH neuron excitability by increasing their action potential firing rate and decreasing the strength of GABA inhibitory inputs, thereby leading to an enhanced GHRH release; and (ii) obestatin counteracts ghrelin actions. Such interactions on GHRH neurons probably participate in the control of GH secretion.

Changes in Growth Hormone-Axis Function in Nutrient Excess or Deprivation

Growth hormone (GH) is produced in a select population of cells, somatotropes, located in the anterior pituitary gland. GH is released into the general circulation where it interacts with multiple peripheral tissues through its receptor, GH receptor, to regulate growth and metabolic function. GH-releasing hormone (GHRH) and somatostatin are the primary positive and negative regulators of GH secretion, respectively. More recently, ghrelin has emerged as an additional stimulatory hormone for GH release. In humans, GH levels decrease in states of nutrient excess, such as obesity, and increase in response to nutrient deprivation, such as fasting, type 1 diabetes, and anorexia nervosa. Considering that GH regulates metabolism of carbohydrate, lipid, and protein, clarifying the mechanisms by which metabolic changes alter pituitary GH synthesis and secretion will increase our knowledge on the pathophysiology and treatment of metabolic diseases. In this review, the effect of nutrient excess and nutrient deficiency on GHaxis function in humans and other mammals will be summarized, with particular emphasis on studies exploring the direct effects of systemic signals, including insulin-like growth factor 1 (IGF-1) and insulin, on somatotrope function. Additionally, new mouse models with somatotrope-specific knockout of IGF-1 and insulin receptors generated by using the Cre/loxP system will be discussed. (Endocrinol Metab 26:279-284, 2011)

Influence of intravenous administration of growth hormone releasing peptide‐2 (GHRP‐2) on detection of growth hormone doping: growth hormone isoform profiles in Japanese male subjects

Administration of exogenous 22 kDa recombinant human growth hormone (rhGH) suppresses the non-22 kDa pituitary growth hormone (GH) secretion by negative feedback; then, the elevated 22 kDa GH to non-22 kDa GH ratio (Rec/Pit ratio) can be utilized to detect doping with rhGH (isoform differential immunoassay). The influence of intravenous administration of growth hormone releasing peptide GHRP-2 on the isoform differential immunoassay for detecting rhGH doping has been investigated.In this study, a reference population (n=100) was used, with 0.04 mg/kg rhGH subcutaneous administration (n=5), 100 μg of GHRP-2 intravenous administration (n=10) and 0.04 mg/kg rhGH combined with 100 μg of GHRP-2 (n=10) in Japanese male subjects. The results indicated that the low dose (0.04 mg/kg) of rhGH led to significantly increased Rec/Pit ratio compared with the Japanese reference limit (P < 0.001). Because GHRP-2 dose led to increases in concentrations of both recombinant GH (recGH) and pituitary GH (pit GH), no significant change in the Rec/Pit ratio was observed (P > 0.05). In a combined administration study, after GHRP-2 dose the Rec/Pit ratios decreased to 39.9-43.9% compared with the elevated ratio caused by the rhGH dose.The results indicated that GHRP-2 administration cannot only be detected by the isoform differential immunoassay but also masks rhGH doping. The analysis of GHRP-2 was found to be suitable for compensating for the disadvantages of the isoform differential immunoassay because GHRP-2 and its metabolite (AA-3) in urine could be detected during the periods of masking of the Rec/Pit ratio by means of liquid chromatography/tandem mass spectrometry.

Novel SNPs of the Caprine Growth Hormone Secretagogue Receptor (GHSR) Gene and Their Association with Growth Traits in Goats

Growth hormone secretagogue receptor (GHSR), a G protein-coupled receptor that binds ghrelin, plays an important role in the central regulation of pituitary growth hormone secretion, food intake, and energy homeostasis. This study analyzed polymorphism of the caprine GHSR gene as a genetic marker candidate for growth traits in goats. Two single nucleotide polymorphisms (GU014697:g.165G-->A and GU014697:g.548T-->C) were identified in exon 2 of the caprine GHSR gene by PCR-single-strand conformation polymorphism and DNA sequencing methods. Their associations with growth traits were analyzed in 313 Xuhuai goats. The results indicated that GU014697:g.548T-->C had significant effects on growth traits. Body length and body length index were significantly higher in individuals with genotype TT than CC and CT in (P < 0.05). TT individuals also tended to have better performance in other traits, such as body height and chest circumference, although there were no statistical differences (P > 0.05). This suggests that GHSR is a strong candidate gene that affects growth traits in goats.

Placental Hormones and the Control of Fetal Growth

Linear growth in the postnatal period is controlled by the production, secretion, and action of pituitary growth hormone and IGF-1. IGF-I and IGF-II production and signaling are also essential for fetal growth and neural development. But the control of IGF production in the fetus is largely independent of GH. Among the factors that control fetal IGF production, the availability and utilization of nutrients is most important. Since fetal nutrient supply ultimately derives from maternal nutrient stores, we can understand fetal growth only through analysis of the factors that control maternal nutrient utilization and transport to the fetus. I will argue that hormones produced by the placenta, including placental lactogen, placental growth hormone, and sex steroids regulate the intake, absorption, utilization and transfer of maternal nutrients to the fetus and modulate fetal and neonatal insulin production. Dysregulation of placental hormone production may be associated with fetal growth retardation or fetal overgrowth and may predispose in later life to glucose intolerance and type 2 diabetes.

The GH–IGF system in amyotrophic lateral sclerosis: correlations between pituitary GH secretion capacity, insulin‐like growth factors and clinical features

The growth hormone (GH) and insulin-like growth factor (IGF) system may be involved in neurodegenerative processes, and some abnormalities have been reported in amyotrophic lateral sclerosis (ALS). Our aim was to investigate the GH-IGF axis in patients with ALS and evaluate correlations between this endocrine system and clinical features. Serum levels of GH, IGF-I, IGF-II, insulin, IGF-binding protein 1 (IGF-BP1), and IGF-binding protein 3 (IGF-BP3) were measured in 25 patients with ALS and 25 age-, gender-, and BMI-matched healthy controls. A GHRH plus arginine test was performed in patients and controls. Clinical status of patients was evaluated with the ALS Functional Rating Scale - Revised (ALSFRS-R) and upper motor neuron (UMN) score. GHRH plus arginine test showed GH deficiency (GHD) in 13 (52%) patients with ALS; severe GHD was found in 6 (24%) and partial GHD in 7 (28%) patients. IGF-I levels were significantly higher in patients with ALS than in healthy controls (182.9 +/- 90.8 vs. 139.4 +/- 58.1 ng/ml; P = 0.015). IGF-I levels were higher in patients with ALS with UMN score >10 than those with UMN score <10 (217.8 +/- 100.8 vs. 155.5 +/- 74.6 ng/ml, P = 0.05). IGF-II levels were significantly lower in patients with ALS than in healthy controls (720.9 +/- 215 vs. 1001.9 +/- 475.4 ng/ml; P = 0.03). The results demonstrate an impairment of the GH-IGFs system in ALS. The degenerative process in ALS might lead to a compensatory increase in IGF-I in an attempt to provide additional support to motor neurons or degenerating muscle fibers. The decrease in IGF-II levels may also be of pathological significance.

Exercise and the Growth Hormone-Insulin-Like Growth Factor Axis

Exercise is a robust physiological stimulator of the pituitary secretion of growth hormone (GH), and within approximately 15 min after the onset of exercise, plasma GH starts to increase. GH and its primary downstream mediator, insulin-like growth factor I (IGF-I), play a critical role in formation, maintenance, and regeneration of skeletal muscles. Consequently, it seems logical to link the exercise-induced stimulation of GH with the hypertrophy observed in exercising muscles. GH stimulates circulating (endocrine) as well as locally produced (peripheral) IGF-I, which acts through autocrine/paracrine mechanisms. However, it remains to be clarified whether skeletal muscle hypertrophy after exercise is stimulated primarily by endocrine or paracrine/autocrine IGF-I. Early cross-sectional studies have observed positive correlations between circulating IGF-I levels and GH secretion, respectively, and indices of fitness. However, longitudinal exercise studies have shown that it is possible to increase muscle strength, performance, and VO2max without concomitant and robust changes in circulating IGF-I, indicating that the effect of exercise on skeletal muscles is mediated via paracrine/autocrine IGF-I rather than endocrine IGF-I. So far, most exercise studies have investigated the concentration of immunoreactive IGF-I in serum or plasma, obtained after extraction of the IGF-binding proteins (i.e., total IGF-I). However, several of the newer exercise studies have included measurement of free IGF-I as well as bioactive IGF-I. The aim of this review was to discuss whether measurement of free and/or bioactive IGF-I have increased our knowledge on the processes that link exercise, muscle hypertrophy, and GH/IGF-I axis. Thus, the current review will discuss (i) the different IGF-I assay methodologies and (ii) the current literature on free, bioactive, and immunoreactive (total) IGF-I in exercising subjects.

Association of polymorphisms of the &amp;lt;i&amp;gt;GHRHR&amp;lt;/i&amp;gt; gene with growth traits in cattle (Brief report)

Abstract. The hypothalamic hormone, growth hormone-releasing hormone (GHRH), is the principal stimulator of pituitary growth hormone (GH) synthesis and secretion. Its pituitary receptor is well characterized as a member of the superfamily of G protein-coupled receptors (MAYO et al., 1992). GHRH and its receptor provide important functions in the regulation of the GH axis and in the development and proliferation of pituitary somatotropes (LIN-SU et al., 2002). By now, polymorphisms of bovine GHRHR were not reported. In the present experiment the 5' flanking region, the coding region and partially introns of GHRHR were screened to detect the SNPs in the predominant cattle breeds of China.

The Pregnancy‐Induced Increase in Baseline Circulating Growth Hormone in Rats is not Induced by Ghrelin

The elevation in baseline circulating growth hormone (GH) that occurs in pregnant rats is thought to arise from increased pituitary GH secretion, but the underlying mechanism remains unclear. Distribution, Fourier and algorithmic analyses confirmed that the pregnancy-induced increase in circulating GH in 3-week pregnant rats was due to a 13-fold increase in baseline circulating GH (P < 0.01), without any significant alteration in the parameters of episodic secretion. Electron microscopy revealed that pregnancy resulted in a reduction in the proportion of mammosomatotrophs (P < 0.01) and an increase in type II lactotrophs (P < 0.05), without any significant change in the somatotroph population. However, the density of the secretory granules in somatotrophs from 3-week pregnant rats was reduced (P < 0.05), and their distribution markedly polarised; the granules being grouped nearest the vasculature. Pituitary GH content was not increased, but steady-state GH mRNA levels declined progressively during pregnancy (P < 0.05). In situ hybridisation revealed that pregnancy was accompanied by a suppression of GH-releasing hormone mRNA expression in the arcuate nuclei (P < 0.05) and enhanced somatostatin mRNA expression in the periventricular nuclei (P < 0.05), an expression pattern normally associated with increased GH feedback. Although gastric ghrelin mRNA expression was elevated by 50% in 3-week pregnant rats (P < 0.01), circulating ghrelin, GH-secretagogue receptor mRNA expression and the GH response to a bolus i.v. injection of exogenous ghrelin were all largely unaffected during pregnancy. Although trace amounts of 'pituitary' GH could be detected in the placenta with radioimmunoassay, significant GH-immunoreactivity could not be observed by immunohistochemistry, indicating that rat placenta itself does not produce 'pituitary' GH. Although not excluding the possibility that the pregnancy-associated elevation in baseline circulating GH could arise from alternative extra-pituitary sources (e.g. the ovary), our data indicate that this phenomenon is most likely to result from a direct alteration of somatotroph function.

Kisspeptin-10 stimulates the secretion of growth hormone and prolactin directly from cultured bovine anterior pituitary cells

Kisspeptins are peptide hormones encoded by the KiSS-1 gene, and act as the principal positive regulator of the reproductive axis by directly stimulating gonadotropin-releasing hormone (GnRH) neuron activity. We recently observed that kisspeptin-10 (the minimal kisspeptin sequence necessary for receptor activation) also has a direct stimulating effect on luteinizing hormone (LH) secretion in bovine anterior pituitary (AP) cells. In the present study, we evaluated the direct effect of kisspeptin-10 on the secretion of other pituitary hormones, growth hormone (GH) and prolactin (PRL), from bovine AP cells. The AP cells, which were prepared from 1- or 8-month-old male calves, were incubated for 2 h with the peptides. Kisspeptin-10 at 100 nM ( P < 0.05), 1000 nM ( P < 0.01) and 10,000 nM ( P < 0.01), but not at 10 nM, significantly stimulated GH secretion from the AP cells of 1-month-old calves, while in 8-month-old calves it was significantly ( P < 0.05) stimulated at 1000 nM ( P < 0.01) and 10,000 nM ( P < 0.01), but not at 10 nM and 100 nM. The response of GH to 100 nM ( P < 0.01), 1000 nM ( P < 0.05) and 10,000 nM ( P < 0.01) kisspeptin-10 in the AP cells of 1-month-old calves was significantly greater than in those of 8-month-old calves. All tested doses of kisspeptin-10 had no effect on PRL secretion from AP cells of 1-month-old calves. However, 1000 nM ( P < 0.05) and 10,000 nM ( P < 0.01), but not lower concentrations, of kisspeptin-10 significantly stimulated PRL secretion from the AP cells of 8-month-old calves. The present study is, as far as we know, the first to examine the direct actions of kisspeptin on the secretion of GH and PRL from the bovine pituitary gland. Further studies are necessary to evaluate the importance of multiple actions of kisspeptin on the pituitary of various animals in vivo.