Stimulated Growth Hormone Release Research Articles

Computational Investigation of the Impact of the Ghrelin Hormone Gene Variation (R51q) on the Hormone-receptor Binding Pattern

Ghrelin is a peptide hormone made up of 28 amino acids. It is involved in various biological processes, including the stimulation of growth hormone release, control of food intake, and metabolic and cytoprotective eff ects. In 1999, this hormone was identifi ed as a ligand for the GHSR1a growth hormone secretagogue receptor. Ghrelin hormone-receptor complexes have been modeled in a few previous in-silico studies, but none of them have investigated the eff ects of the gene variation rs34911341/(R51Q) on the full-length ghrelin model and on the hormone-receptor binding. It was established that the full-length ghrelin model’s secondary structure was unaff ected by the R to Q amino acid substitution. Additionally, the mutant hormone-receptor complex exhibited better outcomes and altered the molecular interactions between the mutant ligand and the receptor by creating novel interactions, according to the post-molecular dynamic simulation analysis.

Heterogeneity of IGF-1 Levels in Children with hCG-Induced Precocious Puberty

Sex steroid stimulates growth hormone release during puberty. However, the role of IGF-1 levels in human-chorionic-gonadotropin-induced precocious puberty remains unclear. A retrospective study reviewing thirty patients with precocious puberty due to human-chorionic-gonadotropin-secreting intracranial germ cell tumors was performed. Changes in IGF-1 levels were collected. All patients included were boys. At diagnosis, the median IGF-1 standard deviation was 0.87 (0.1, 1.87). When human-chorionic-gonadotropin normalized, the median IGF-1 standard deviation was 1.58 (-0.53, 2.55), which is slightly higher than baseline (p = 0.408). When patients completed their therapeutic plan, the median IGF-1 standard deviation was 0.10 (-1.05, 0.68), which was significantly lower than that of baseline (p = 0.004) and of human-chorionic-gonadotropin being normalized (p = 0.003). At the last visit, the mean IGF-1 standard deviation was -1.11(-1.97, 0.76), which is slightly lower than that of baseline (p = 0.109) and post-therapy levels (p = 0.575), but significantly lower than that of human-chorionic-gonadotropin being normalized. Two patients had IGF-1 levels above 2 standard deviations at diagnosis, eight at the time when human-chorionic-gonadotropin normalized, and two at the end of therapy. Only one patient had an IGF-1 level below 2 standard deviations at diagnosis and at the time when human-chorionic-gonadotropin normalized, and two patients at the end of therapy. At the last follow-up, all patients had normal IGF-1 levels. IGF-1 levels in patients with human-chorionic-gonadotropin-induced precocious puberty have heterogeneity, but IGF-1 standard deviations are mostly within the normal range. If elevated, it might decline later with a decrease in human-chorionic-gonadotropin level. IGF-1 levels seem not valuable enough to assess human-chorionic-gonadotropin-induced precocity regression.

ODP313 Glucagon-Stimulated Copeptin Measurements in the Differential Diagnosis of Diabetes Insipidus: A Double-Blind Randomized Placebo-Controlled Study

Abstract Background The differential diagnosis of diabetes insipidus and primary polydipsia is challenging. To date, the most reliable approaches are copeptin measurement after hypertonic saline infusion or arginine, which is a known growth hormone secretagogue but has recently also been shown to stimulate the neurohypophysis. Similar to arginine, glucagon is also known to stimulate growth hormone release, but its effect on the neurohypophysis unknown. Methods In this double-blind, randomized, placebo-controlled trial, we enrolled 22 healthy participants, 10 patients with central diabetes insipidus and 10 patients with primary polydipsia at the University Hospital Basel. Each participant underwent the glucagon test, i. e., subcutaneous injection of 1mg glucagon, and placebo test, i. e., subcutaneous injection of 1 ml 0.9% sodium. Plasma copeptin levels were measured at baseline and 30, 60, 90, 120, 150, 180 minutes after injection. The primary objective was to determine whether glucagon stimulates copeptin and to explore whether the copeptin response differentiates between diabetes insipidus and primary polydipsia. Findings: The median (IQR) age of all participants was 27 years (23; 32), 59% were female. In healthy participants, glucagon injection stimulated copeptin with a median (IQR) increase of 7.56 (2.38; 28. 03) pmol/l, while placebo had no effect (0.10pmol/l (-0.70; 0.68); difference: 7.67 (1.98, 27. 09) pmol/l, p < 0. 001). In patients with central diabetes insipidus, copeptin showed no relevant increase after glucagon injection, with an increase of 0.55pmol/l (0.21; 1.65), whereas copeptin was stimulated in patients with primary polydipsia with an increase of 15.70 (5.99; 24.39) pmol/l. Using a copeptin cutoff level of 4.6pmol/l had a sensitivity of 100% (95%CI 100-100) and a specificity of 90% (95%CI 70-100) to discriminate between diabetes insipidus and primary polydipsia. Interpretation: Glucagon stimulates the neurohypophysis, and glucagon-stimulated plasma copeptin has the potential to be used for a safe, novel, and precise test in the differential diagnosis of polyuria-polydipsia syndrome. Presentation: No date and time listed

Glucagon-stimulated copeptin measurements in the differential diagnosis of diabetes insipidus: a double-blind, randomized, placebo-controlled study.

The differential diagnosis of diabetes insipidus is challenging. The most reliable approaches are copeptin measurements after hypertonic saline infusion or arginine, which is a known growth hormone secretagogue but has recently also been shown to stimulate the neurohypophysis. Similar to arginine, glucagon stimulates growth hormone release, but its effect on the neurohypophysis is poorly studied. Double-blind, randomized, placebo-controlled trial including 22 healthy participants, 10 patients with central diabetes insipidus, and 10 patients with primary polydipsia at the University Hospital Basel, Switzerland. Each participant underwent the glucagon test (s.c. injection of 1 mg glucagon) and placebo test. The primary objective was to determine whether glucagon stimulates copeptin and to explore whether the copeptin response differentiates between diabetes insipidus and primary polydipsia. Copeptin levels were measured at baseline, 30, 60, 90, 120, 150, and 180 min after injection. In healthy participants, glucagon stimulated copeptin with a median increase of 7.56 (2.38; 28.03) pmol/L, while placebo had no effect (0.10 pmol/L (-0.70; 0.68); P < 0.001). In patients with diabetes insipidus, copeptin showed no relevant increase upon glucagon, with an increase of 0.55 (0.21; 1.65) pmol/L, whereas copeptin was stimulated in patients with primary polydipsia with an increase of 15.70 (5.99; 24.39) pmol/L. Using a copeptin cut-off level of 4.6pmol/L had a sensitivity of 100% (95% CI: 100-100) and a specificity of 90% (95% CI: 70-100) to discriminate between diabetes insipidus and primary polydipsia. Glucagon stimulates the neurohypophysis, and glucagon-stimulated copeptin has the potential for a safe, novel, and precise test in the differential diagnosis of diabetes insipidus.

GLP-1 receptor agonists stimulate growth hormone release

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Vitamin D content in children with short stature due to intrauterine growth restriction against normosomatotropinemia

Background. There are no data about the status of vitamin D and its effect on the growth hormone/growth factors axis in prepubertal children with intrauterine growth restriction (IGR). Of particular interest is a group of patients who remain significantly short on the background of a decrease in insulin-like growth factor 1 (IGF-1) levels and normal stimulated release of growth hormone (GH). The purpose of our study was to determine the levels of 25-hydroxycalciferol in the blood plasma of prepubertal children with short stature due to IGR on the background of normosomatotropinemia. Materials and methods. We examined 34 prepubertal children (14 girls and 20 boys) with short stature (average age — 6.95 ± 0.46 years) who had signs of IGR at birth. A symmetrical type of IGR was found in 15 (44.2 %) patients, an asymmetrical type — in 19 (55.8 %). According to the results of functional tests all patients had a normal GH peak release (&gt; 10 ng/ml). Thyroid-stimulating hormone, free thyroxine levels in the blood plasma were determined by the immunoradiometric assay with standard Immunotech® kit (Czech Republic). At the time of examination, all patients were euthyroid. GH, IGF-1 and insulin-like growth factor binding protein 3 (IGFBP-3) levels were determined by enzyme-linked immunosorbent assay using Immulite 2000 Xi kits (Siemens, USA). 25-hydroxycalciferol level was determined by the immunochemiluminescent method (Abbott, USA). The results were evaluated according to the guidelines of the International Society of Endocrinology (2011). Results. It was found that in prepubertal children with IGR signs at birth, the average height standard deviation score (SDS) at the time of the examination was –2.83 ± 0.12. There were no significant differences between the height and body weight in patients with a symmetrical and an asymmetrical types of IGR at the time of examination (p &gt; 0.05). Vitamin D content in the blood plasma of children with IGR signs was 49.70 ± 2.17 nmol/l in the whole group. Vitamin D insufficiency below 75 nmol/l was found in 16 (47 %) patients, and vitamin D deficiency below 50 nmol/l — in 18 (53 %). No significant differences were found between vitamin D values in girls and boys with signs of IGR (51.79 ± 3.38 nmol/l and 48.36 ± 2.86 nmol/l, respectively, p &gt; 0.05). Height SDS in the group of patients with an asymmetrical type of IGR weakly correlates (r = 0.38) with vitamin D content. Vitamin D level significantly differed depending on IGR type (in a symmetrical type — 44.1 ± 3.2 nmol/l, in an asymmetrical type — 54.20 ± 2.56 nmol/l, p &lt; 0.05). IGF-1 SDS in the group of patients with an asymmetrical type of IGR weakly correlated (r = 0.36) with vitamin D level. On the background of a significant decrease in IGFBP-3 content in children with an asymmetrical type of IGR compared to those with a symmetrical type (–1.32 ± 0.07 SDS and –1.00 ± 0.14 SDS, p &lt; 0.05), there was a reduction in IGF-1 levels (–1.62 ± 0.10 SDS and –1.34 ± 0.14 SDS, p = 0.05). Conclusions. Patients born with signs of IGR, even against normosomatotropinemia, may still have significant growth deficit, a sharp decrease in IGF-1 and IGFBP-3 for a long time after birth. The results obtained indicate the presence of hypovitaminosis D in all prepubertal patients who were born with the signs of intrauterine growth restriction. No correlation was found between vitamin D level and the maximum peak of stimulated growth hormone release. However, patients with an asymmetrical type of IGR have a weak correlation (r = 0.36) between IGF-1 SDS and vitamin D content, a significant decrease in the content of IGF-1, IGFBP-3, as well as vitamin D compared to its level in a symmetrical type of IGR. It is recommended to include the determination of vitamin D level in the blood plasma irrespective of the type of disease and the state of somatotropic function in the list of studies for the examination of children with short stature who were born with signs of intrauterine growth restriction.

LEAP-2: An Emerging Endogenous Ghrelin Receptor Antagonist in the Pathophysiology of Obesity.

Liver-expressed antimicrobial peptide 2 (LEAP-2), originally described as an antimicrobial peptide, has recently been recognized as an endogenous blocker of growth hormone secretagogue receptor 1a (GHS-R1a). GHS-R1a, also known as ghrelin receptor, is a G protein-coupled receptor (GPCR) widely distributed on the hypothalamus and pituitary gland where it exerts its major functions of regulating appetite and growth hormone (GH) secretion. The activity of GHS-R1a is controlled by two counter-regulatory endogenous ligands: Ghrelin (activation) and LEAP-2 (inhibition). Ghrelin activates GHS-R1a on the neuropeptide Y/Agouti-related protein (NPY/AgRP) neurons at the arcuate nucleus (ARC) to promote appetite, and on the pituitary somatotrophs to stimulate GH release. On the flip side, LEAP-2, acts both as an endogenous competitive antagonist of ghrelin and an inverse agonist of constitutive GHS-R1a activity. Such a biological property of LEAP-2 vigorously blocks ghrelin’s effects on food intake and hormonal secretion. In circulation, LEAP-2 displays an inverse pattern as to ghrelin; it increases with food intake and obesity (positive energy balance), whereas decreases upon fasting and weight loss (negative energy balance). Thus, the LEAP-2/ghrelin molar ratio fluctuates in response to energy status and modulation of this ratio conversely influences energy intake. Inhibiting ghrelin’s activity has shown beneficial effects on obesity in preclinical experiments, which sheds light on LEAP-2’s anti-obesity potential. In this review, we will analyze LEAP-2’s effects from a metabolic point of view with a focus on metabolic hormones (e.g., ghrelin, GH, and insulin), and discuss LEAP-2’s potential as a promising therapeutic target for obesity.

Current concepts of the diagnosis of adult growth hormone deficiency

In adults, growth hormone (GH) deficiency is associated with increased visceral adiposity, decreased lean body mass, bone mineral density and exercise capacity, dyslipidemia, insulin resistance, increased cardiometabolic and fracture risk, and impaired quality of life. The aim of the present article is to review the diagnosis of GH deficiency in adults. To avoid overdiagnosis of GH deficiency, it is critical to evaluate only patients at risk for pituitary dysfunction, including those who have had sellar masses, pituitary surgery, radiation therapy, traumatic brain injury, subarachnoid hemorrhage or childhood onset GH deficiency. Evaluation for GH deficiency should be undertaken after testing and replacement of other pituitary hormone deficits. Since GH secretion is pulsatile, measuring serum GH levels randomly is not helpful in establishing the diagnosis of GH deficiency. Serum insulin-like growth factor I (IGF-I) levels lack substantial diurnal variation but also lack sufficient sensitivity and specificity in the diagnosis of GH deficiency in adults. However, adults with multiple (≥3) additional pituitary hormone deficiencies, risk factors for hypopituitarism and low serum IGF-I levels are very likely to be GH deficient. In most cases, the diagnosis of GH deficiency requires stimulation testing. These tests involve the administration of a pharmacologic agent that normally stimulates GH release from pituitary somatotrophs, including insulin, glucagon, growth hormone releasing hormone-arginine or macimorelin, followed by sampling of serum specimens at regular intervals for GH assay. Patients with a peak GH level that is below a predetermined cutpoint are classified as GH deficient. A systematic approach to the diagnosis of GH deficiency is essential in order to accurately identify adults who may benefit from GH replacement.

Three-dimensional growth of breast cancer cells potentiates the anti-tumor effects of unacylated ghrelin and AZP-531

Breast cancer is the most common type of cancer in women and notwithstanding important therapeutic advances, remains the second leading cause of cancer-related death. Despite extensive research relating to the hormone ghrelin, responsible for the stimulation of growth hormone release and appetite, little is known of the effects of its unacylated form, especially in cancer. The present study aimed to characterize effects of unacylated ghrelin on breast cancer cells, define its mechanism of action, and explore the therapeutic potential of unacylated ghrelin or analog AZP-531. We report potent anti-tumor effects of unacylated ghrelin, dependent on cells being cultured in 3D in a biologically-relevant extracellular matrix. The mechanism of unacylated ghrelin-mediated growth inhibition involves activation of Gαi and suppression of MAPK signaling. AZP-531 also suppresses the growth of breast cancer cells in vitro and in xenografts, and may be a novel approach for the safe and effective treatment of breast cancer.

Thyrotropin-Releasing Hormone (TRH) and Somatostatin (SST), but not Growth Hormone-Releasing Hormone (GHRH) nor Ghrelin (GHRL), Regulate Expression and Release of Immune Growth Hormone (GH) from Chicken Bursal B-Lymphocyte Cultures.

It is known that growth hormone (GH) is expressed in immune cells, where it exerts immunomodulatory effects. However, the mechanisms of expression and release of GH in the immune system remain unclear. We analyzed the effect of growth hormone-releasing hormone (GHRH), thyrotropin-releasing hormone (TRH), ghrelin (GHRL), and somatostatin (SST) upon GH mRNA expression, intracellular and released GH, Ser133-phosphorylation of CREB (pCREBS133), intracellular Ca2+ levels, as well as B-cell activating factor (BAFF) mRNA expression in bursal B-lymphocytes (BBLs) cell cultures since several GH secretagogues, as well as their corresponding receptors (-R), are expressed in B-lymphocytes of several species. The expression of TRH/TRH-R, ghrelin/GHS-R1a, and SST/SST-Rs (Subtypes 1 to 5) was observed in BBLs by RT-PCR and immunocytochemistry (ICC), whereas GHRH/GHRH-R were absent in these cells. We found that TRH treatment significantly increased local GH mRNA expression and CREB phosphorylation. Conversely, SST decreased GH mRNA expression. Additionally, when added together, SST prevented TRH-induced GH mRNA expression, but no changes were observed in pCREBS133 levels. Furthermore, TRH stimulated GH release to the culture media, while SST increased the intracellular content of this hormone. Interestingly, SST inhibited TRH-induced GH release in a dose-dependent manner. The coaddition of TRH and SST decreased the intracellular content of GH. After 10 min. of incubation with either TRH or SST, the intracellular calcium levels significantly decreased, but they were increased at 60 min. However, the combined treatment with both peptides maintained the Ca2+ levels reduced up to 60-min. of incubation. On the other hand, BAFF cytokine mRNA expression was significantly increased by TRH administration. Altogether, our results suggest that TRH and SST are implicated in the regulation of GH expression and release in BBL cultures, which also involve changes in pCREBS133 and intracellular Ca2+ concentration. It is likely that TRH, SST, and GH exert autocrine/paracrine immunomodulatory actions and participate in the maturation of chicken BBLs.

GLUTAMINE SUPPLEMENTATION: EFFECTS ON GROWTH HORMONE AND TIME-TRIAL PERFORMANCE AFTER PROLONGED EXERCISE

Dietary glutamine supplementation has been proposed as a potential aid to athletic performance. The purpose of the investigation was to determine if glutamine supplementation might improve cycling performance, perhaps by stimulating growth hormone release, in athletes consuming a high-carbohydrate diet. Six trained young adult men participated in two four-day supplementation trials. In both trials, the subjects underwent an identical carbohydrate-loading regimen of controlled diet (75% carbohydrate) and exercise. The only difference in the trials was whether the subjects ingested dietary supplements of glutamine or glucose placebo. During the first three days of each trial, the diets were supplemented with either glutamine or glucose placebo at a dosage of 150 mg/kg body weight (~10.4 g/d). On the fourth day, the supplements were dissolved in a sports drink (4 g/L). The sports drink initially contained a 6% solution of carbohydrate. On the fourth day the subjects ingested 7 ml/kg of the supplemented sports drink 2 h before exercise, 5 ml/kg 1 h before exercise, and 3 ml/kg after 15, 30, 45, 60, and 90 min of exercise. The total amount of glutamine supplement or placebo consumed on the fourth day was 108 mg/kg or about 7.4 g, of which 3.3 g were consumed before and 4.1 g during exercise. On the fourth day, subjects completed 90 min of cycle ergometry, divided into six 15-min periods, each of which included in sequence 12 min @75% VO2max, 1 min @ 120% VO2max, and 2 min @ 50% VO2max. The 90 min exercise session was immediately followed by 15 min of rest and then a final 20-km time trial at ~85% VO2max. Plasma concentrations of glycerol and free fatty acids and serum growth hormone concentrations were measured before and during exercise, and time-trial performance was recorded. Times (± SEM) to complete the 20-km performance rides were 31.03 ± 0.58 min for the placebo trial and 30.93 ± 0.60 min for the glutamine trial and were not significantly different (P&gt;0.05). There were also no significant effects on serum growth hormone or on plasma glycerol or free fatty acids attributable to glutamine supplementation at any sampling time. In summary, we found no evidence that glutamine supplementation in moderate dosages has any effect on circulating growth hormone, glycerol, or free fatty acids or on time-trial performance in athletes who consume a high-carbohydrate diet

Ghrelin receptor in agouti-related peptide neurones regulates metabolic adaptation to calorie restriction.

Ghrelin is a gut hormone that signals to the hypothalamus to stimulate growth hormone release, increase food intake and promote fat deposition. The ghrelin receptor, also known as growth hormone secretagogue receptor (GHS-R), is highly expressed in the brain, with the highest expression in agouti-related peptide (AgRP) neurones in the hypothalamus. Compelling evidence indicates that ghrelin serves as a survival hormone with respect to maintaining blood glucose and body weight during nutritional deficiencies. Recent studies have demonstrated that AgRP neurones are involved in metabolic and behavioural adaptation to an energy deficit to improve survival. In the present study, we used a neuronal subtype-specific GHS-R knockout mouse (AgRP-Cre;Ghsrf/f ) to investigate the role of GHS-R in hypothalamic AgRP neurones in metabolic and behavioural adaptation to hypocaloric restricted feeding. We subjected the mice to a restricted feeding regimen of 40% mild calorie restriction (CR), with one-quarter of food allotment given in the beginning of the light cycle and three-quarters given at the beginning of the dark cycle, to mimic normal mouse intake pattern. The CR-fed AgRP-Cre;Ghsrf/f mice exhibited reductions in body weight, fat mass and blood glucose. Metabolic profiling of these CR-fed AgRP-Cre;Ghsrf/f mice showed a trend toward reduced basal metabolic rate, significantly reduced core body temperature and a decreased expression of thermogenic genes in brown adipose tissue. This suggests a metabolic reset to a lower threshold. Significantly increased physical activity, a trend toward increased food anticipatory behaviour and altered fuel preferences were also observed in these mice. In addition, these CR-fed AgRP-Cre;Ghsrf/f mice exhibited a decreased counter-regulatory response, showing impaired hepatic glucose production. Lastly, hypothalamic gene expression in AgRP-Cre;Ghsrf/f mice revealed increased AgRP expression and a decreased expression of genes in β-oxidation pathways. In summary, our data suggest that GHS-R in AgRP neurones is a key component of the neurocircuitry involved in metabolic adaptation to calorie restriction.

Myostatin regulates pituitary development and hepatic IGF1.

Circulating myostatin-attenuating agents are being developed to treat muscle-wasting disease despite their potential to produce serious off-target effects, as myostatin/activin receptors are widely distributed among many nonmuscle tissues. Our studies suggest that the myokine not only inhibits striated muscle growth but also regulates pituitary development and growth hormone (GH) action in the liver. Using a novel myostatin-null label-retaining model (Jekyll mice), we determined that the heterogeneous pool of pituitary stem, transit-amplifying, and progenitor cells in Jekyll mice depletes more rapidly after birth than the pool in wild-type mice. This correlated with increased levels of GH, prolactin, and the cells that secrete these hormones, somatotropes and lactotropes, respectively, in Jekyll pituitaries. Recombinant myostatin also stimulated GH release and gene expression in pituitary cell cultures although inhibiting prolactin release. In primary hepatocytes, recombinant myostatin blocked GH-stimulated expression of two key mediators of growth, insulin-like growth factor (IGF)1 and the acid labile subunit and increased expression of an inhibitor, IGF-binding protein-1. The significance of these findings was demonstrated by smaller muscle fiber size in a model lacking myostatin and liver IGF1 expression (LID-o-Mighty mice) compared with that in myostatin-null (Mighty) mice. These data together suggest that myostatin may regulate pituitary development and function and that its inhibitory actions in muscle may be partly mediated by attenuating GH action in the liver. They also suggest that circulating pharmacological inhibitors of myostatin could produce unintended consequences in these and possibly other tissues.

New Insights on Neuronal Functions of Ghrelin Receptor GHS-R in Obesity

Obesity is defined as excessive fat accumulation caused by the imbalance of energy intake versus expenditure. Low-grade chronic inflammation is a hallmark of obesity, and it is closely linked to insulin resistance. Obesity-induced inflammation and its associated metabolic dysfunctions underlay pathological processes of many chronic diseases such as insulin resistance, diabetes, sarcopenia and cardiovascular disease. Ghrelin is the only known circulating orexigenic hormone; it stimulates growth hormone release, and increases adiposity and insulin resistance. Ghrelin’s functions are mediated through its receptor, growth hormone secretagogue receptor (GHS-R). The brain plays a critical role in energy homeostasis and energy metabolism. GHS-R is primarily expressed in the brain; the brain is a key ghrelin targeting site. The current review discusses the insights we have gained from global GHS-R knockout mice and neural conditional GHS-R knockout mice, specifically involving the roles of GHS-R in food intake, feeding adaptation, thermogenesis, meta-inflammation, and physical activity.

Ghrelin stimulates growth hormone release from the pituitary via hypothalamic growth hormone-releasing hormone neurons in the cichlid, Oreochromis niloticus.

Ghrelin, a gut-brain peptide hormone, is implicated in a multiplicity of biological functions, including energy homeostasis and reproduction. Neuronal systems that are involved in energy homeostasis as well as reproduction traverse the hypothalamus; however, the mechanism by which they control energy homeostasis is not fully understood. The present study analyzes the anatomical relationship of neurons expressing gonadotropin-releasing hormone (GnRH), neuropeptide Y (NPY) and growth hormone-releasing hormone (GHRH) in a cichlid, tilapia (Oreochromis niloticus). Additionally, we examine in vivo effects of ghrelin on these hypothalamic neurons and plasma growth hormone (GH) and insulin-like growth factor-1 (IGF-1) levels. Double-immunofluorescence showed neuronal fiber associations between GnRH, NPY and GHRH in the brain and pituitary. Intracerebroventricular injection of ghrelin had no effect on numbers, soma size, or optical density of GnRH and NPY neurons, whereas the number of GHRH neurons was significantly decreased in the animals injected with ghrelin when compared to controls, which may indicate administered ghrelin promoted GHRH release. Plasma GH and pituitary GH mRNA levels were significantly increased in the animals injected with ghrelin. These results suggest that central administration of ghrelin primarily act on hypothalamic GHRH neurons to stimulate GH release from the pituitary in the tilapia.

Obestatin stimulates the somatotrophic axis activity in sheep

The effects of obestatin (an anorexigenic peripheral peptide) on somatotrophic axis activity in ruminants have not yet been determined. The aim of this study was to investigate the consequence of intracerebroventricular infusions of obestatin on the activity of the somatotrophic axis in peripubertal female sheep. Animals were randomly divided into two groups: control group received intracerebroventricular infusions of the vehicle, and the obestatin group was infused with obestatin (25 µg/120 µL h−1). The series of four hourly infusions on three consecutive days were performed. The blood samples were collected on day 0 and on day 3. Immediately after the end of experiment sheep were slaughtered. Parts of the brains were fixed in situ for further immunohistochemical analysis, while the remaining brains were frozen for Real Time RT-qPCR analysis.Substantial changes in the activity of the somatotrophic axis were observed in obestatin-infused sheep. In those animals obestatin evoked an increase in growth hormone-releasing hormone (GHRH) mRNA expression and a decrease in somatostatin mRNA expression in the anterior hypothalamic area. Moreover, a decrease in somatostatin immunoreactivity in the periventricular nucleus and an increase in somatostatin immunopositive fibers in the median eminence were noted. Changes in the GHRH and somatostatin activity are associated with an increase in growth hormone (GH) gene expression and in the amount of GH immunoreactive material stored in the somatotrophic pituitary cells. Consequently, an increase in GH concentration in the peripheral blood, due to an increase in the number of pulses was observed.It was revealed that obestatin affects the somatostatin/GHRH/GH system at the level of protein synthesis, accumulation and release. It is suggested that obestatin participates in the mechanism modulating somatotrophic axis activity at the central level by stimulating GH release through suppression of somatostatin output. Thereby, it can be concluded that obestatin may be involved in the modulation of growth processes in sheep.

Kisspeptin Stimulates Growth Hormone Release by Utilizing Neuropeptide Y Pathways and Is Dependent on the Presence of Ghrelin in the Ewe.

Although kisspeptin is the primary stimulator of gonadotropin-releasing hormone secretion and therefore the hypothalamic-pituitary-gonadal axis, recent findings suggest kisspeptin can also regulate additional neuroendocrine processes including release of growth hormone (GH). Here we show that central delivery of kisspeptin causes a robust rise in plasma GH in fasted but not fed sheep. Kisspeptin-induced GH secretion was similar in animals fasted for 24 hours and those fasted for 72 hours, suggesting that the factors involved in kisspeptin-induced GH secretion are responsive to loss of food availability and not the result of severe negative energy balance. Pretreatment with the neuropeptide Y (NPY) Y1 receptor antagonist, BIBO 3304, blocked the effects of kisspeptin-induced GH release, implicating NPY as an intermediary. Kisspeptin treatment induced c-Fos in NPY and GH-releasing hormone (GHRH) cells of the arcuate nucleus. The same kisspeptin treatment resulted in a reduction in c-Fos in somatostatin (SS) cells in the periventricular nucleus. Finally, blockade of systemic ghrelin release or antagonism of the ghrelin receptor eliminated or reduced the ability of kisspeptin to induce GH release, suggesting the presence of ghrelin is required for kisspeptin-induced GH release in fasted animals. Our findings support the hypothesis that during short-term fasting, systemic ghrelin concentrations and NPY expression in the arcuate nucleus rise. This permits kisspeptin activation of NPY cells. In turn, NPY stimulates GHRH cells and inhibits SS cells, resulting in GH release. We propose a mechanism by which kisspeptin conveys reproductive and hormone status onto the somatotropic axis, resulting in alterations in GH release.

Suppression of GHS-R in AgRP Neurons Mitigates Diet-Induced Obesity by Activating Thermogenesis.

Ghrelin, an orexigenic hormone released primarily from the gut, signals the hypothalamus to stimulate growth hormone release, enhance appetite and promote weight gain. The ghrelin receptor, aka Growth Hormone Secretagogue Receptor (GHS-R), is highly expressed in the brain, with highest expression in Agouti-Related Peptide (AgRP) neurons of the hypothalamus. We recently reported that neuron-specific deletion of GHS-R completely prevents diet-induced obesity (DIO) in mice by activating non-shivering thermogenesis. To further decipher the specific neuronal circuits mediating the metabolic effects of GHS-R, we generated AgRP neuron-specific GHS-R knockout mice (AgRP-Cre;Ghsrf/f). Our data showed that GHS-R in AgRP neurons is required for ghrelin’s stimulatory effects on growth hormone secretion, acute food intake and adiposity, but not for long-term total food intake. Importantly, deletion of GHS-R in AgRP neurons attenuated diet-induced obesity (DIO) and enhanced cold-resistance in mice fed high fat diet (HFD). The HFD-fed knockout mice showed increased energy expenditure, and exhibited enhanced thermogenic activation in both brown and subcutaneous fat; this implies that GHS-R suppression in AgRP neurons enhances sympathetic outflow. In summary, our results suggest that AgRP neurons are key site for GHS-R mediated thermogenesis, and demonstrate that GHS-R in AgRP neurons plays crucial roles in governing energy utilization and pathogenesis of DIO.

L-Ornithine stimulates growth hormone release in a manner dependent on the ghrelin system.

We found that intraduodenal administration of l-ornithine (l-Orn) stimulates growth hormone (GH) secretion in Wistar rats, and then investigated its mechanism. GH-releasing activity after intraduodenal administration of l-Orn was blocked by [d-Lys3]-GHRP-6, an antagonist of the ghrelin receptor; however, l-Orn (100 μM) has no affinity for the ghrelin receptor, suggesting that the GH-releasing activity of l-Orn is mediated via ghrelin release and activation of the ghrelin receptor. Intraduodenally administered l-Orn increased ghrelin mRNA expression in the duodenum but not in the stomach or hypothalamus. In addition, l-Orn-induced GH-releasing activity was inhibited by propranolol, an antagonist of β-adrenergic receptor, which is known to be coupled to ghrelin release. In conclusion, intraduodenally administered l-Orn stimulates GH secretion through the sympathetic nervous and ghrelin systems.

JMV2894, a novel growth hormone secretagogue, accelerates body mass recovery in an experimental model of cachexia.

Oncologic patients subjected to chemotherapy frequently present aphagia, malnutrition, and cachexia. The purpose of this study was to investigate whether selected growth hormone secretagogues including hexarelin, JMV2894 and JMV2951 could antagonize body weight loss and wasting induced by cisplatin administration in rats. The three growth hormone secretagogues behaved as full agonists of the growth hormone secretagogues receptor both in terms of ability to stimulate calcium mobilization in Chinese hamster ovary cells and stimulation of growth hormone release in neonatal rats. Adult rats were (i) treated with vehicle throughout (controls), or (ii) treated with cisplatin (days 1-3) and a growth hormone secretagogues or vehicle, (days 1-12). Body weight and food consumption were measured daily. Although all growth hormone secretagogues caused initial transient acute increases in food intake, the total amount of food eaten by controls and growth hormone secretagogues treated groups over the 12 experimental days was not significantly different. All groups pre-treated with cisplatin lost up to 5-10 % body weight in the first 4 days; they subsequently gained weight at a rate comparable with controls. Interestingly, rats which received JMV2894 demonstrated a faster gain in body weight than any other growth hormone secretagogues treated group and at the end of the protocol reached a weight similar to that of controls. JMV2894 did not stimulate perirenal and epididymal fat accumulation but reduced MuRF mRNA levels in skeletal muscles. In conclusion, our findings demonstrate that JMV2894 antagonizes cisplatin induced weight loss in rats and may prove useful in antagonizing cachexia associated with cancer and chemotherapy in humans.