GH-releasing Activity Research Articles

A quantitative UHPLC-MS/MS method for the growth hormone-releasing peptide-6 determination in complex biological matrices and transdermal formulations

Growth hormone-releasing peptide-6 (GHRP-6) is part of a group of small synthetic peptides with potent GH-releasing activity that have gained attention in the last two decades by virtue of their cyto- and cardioprotective effects. Despite numerous preclinical studies highlighting the potential cardiovascular benefits of GHRP-6, confirmation of clinical efficacy is still awaited. Recent advances in transdermal drug delivery systems have been made to address challenges related to the poor skin permeation rate of peptides by using pain-free microneedle (MN) devices. Accordingly, highly sensitive and validated analytical methods are required for the potential clinical translation of MN-based peptides. The ultra-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) methods developed in this study aimed to quantify GHRP-6 in biological matrices (plasma, skin) and dissolving polymeric MNs. UHPLC/MS-MS method detection limits of 0.1, 1.1, 0.9 and 1.5 ng/mL were achieved in neat solution, plasma, MN polymer solution, and skin matrices, respectively. Method validation also involved assessment of precision, accuracy, limits of quantification, linearity of matched calibration curves (R2 > 0.990), extraction recovery, matrix effect, stability studies, selectivity, and carry-over effect. Additionally, quality control samples were analyzed at three concentration levels to determine recovery (85–109%) and accuracy/bias (3.2–14.7%). Intra- and inter-day precision were within the range of acceptance (RSDs of 3.0–13.9% and 0.4–14.5%, respectively). The validity and applicability of such methods were successfully demonstrated for transdermal GHRP-6 delivery using GHRP-6-loaded MN patches applied to pig skin.

P0519HEXARELIN PROTECTS ISCHEMIA REPERFUSION INDUCED ACUTE KIDNEY INJURY BY TARGETING 14-3-3Σ

Abstract Background and Aims Acute kidney injury (AKI), manifested as a sudden decline in renal function on the order of days or a week, is one of the most common complications and is strongly associated with renal prognosis, medical expenses and length of stay of hospitalized patients. However, incidence of AKI can be reduced by early intervention. Hexarelin is a synthetic analogue of ghrelin with a potent GH releasing activity, which is also found to exhibited a significant protectant activity against postischemic ventricular dysfunction in isolated perfused hearts subjected to low flow ischemia and reperfusion. This study aims to explore the effects of hexarelin on ischemia reperfusion induced acute kidney injury (I/R-AKI) and the underlying mechanism of it. Method Thirty healthy male SPF SD aged at 8 weeks weighing 250-300g rats were divided into 5 groups including normal group, sham operation group, acute kidney injury (AKI) group, acute kidney injury group after hexarelin (HEX + AKI), and acute kidney injury group after saline (Saline + AKI). Bilateral kidney artery clamping was applied for 50 min to induce AKI. The drug-administered group and the saline-controlled group rats were treated with intraperitoneal injections 7 days before modelling and the Hex + AKI group and the saline + AKI group were given Hexarelin (dose 100 μg/kg. d) and equal volume of saline, respectively. To explore the underlying mechanism of HEX on I/R-AKI, gene expression profiling of AKI samples were searched from Pubmed, GEO dataset. Differential expression genes were used to predict canonical signal transduction pathways and signalling networks. Molecular docking was used to predict the combination of hub proteins and HEX. Results 1) Renal function in HEX-pretreated rats was significantly improved compared with control group: HE results showed that renal tubules were less dilated and rebuilt after pretreatment, and the infiltration area was significantly reduced; serum creatinine (P = 0.0005 <0.05), urea nitrogen (P <0.0001) concentration were significantly reduced; RT-qPCR showed that relative expression of Kim-1 (P<0.0001), caspase3 (P = 0.007), Bax (P <0.0001), Bad (P = 0.0168 <0.05) in HEX+AKI group were significantly decreased while the relative expression of Bcl-2 (P <0.05) was significantly increased compared with saline treated rats; 2) Microarray data analysis showed that 63 differential expression genes including SFN, Cyr61, Kim-1 were hub genes in the development of I/R-AKI; 3) Three-dimensional structure of the hub proteins HEX were obtained from the SWISS-MODEL database and the PubChem compound database, and Autodock software was used to calculate the molecular docking between proteins and HEX. Results showed that HEX and the protein that encoded by the gene SFN (SFN, 14-3-3σ) binding stably with a binding energy of -8.51; Conclusion Hexarelin protects ischemia reperfusion induced acute kidney injury by targeting 14-3-3σ.

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.

Regulation of Growth Hormone by the Splanchnic Area.

The regulation of growth hormone (GH) was traditionally thought to be under the control of two main hypothalamic neuropeptides; GH-releasing hormone and somatostatin. In 1999, with the isolation of ghrelin, as a gastric-derived peptide with potent GH-releasing activity, concept of regulation of the somatotropic axis completely changed. In addition to its GH-releasing activity, ghrelin exhibited the capacity to modulate food intake and body weight. The role of this splanchnic factor in regulating GH as a nexus of energy balance control and GH are explored in this chapter. From a physiological standpoint, a novel mechanism of GH regulation mediated by ghrelin exists, implicating the peripheral modulation of the cannabinoid receptor.

The effect of ghrelin and estradiol on mean concentration of thyroid hormones.

Background:Ghrelin is a novel peptide hormone that has GH releasing activity and also other endocrine and metabolic functions. It can also increase food intake and decrease T3 and T4 concentrations. Several parameters of hypothalamic-pituitary-thyroid (HPT) axis function are modulated by 17β-estradiol (E2).Objectives:The purpose of this study was to investigate the effect of interactions between ghrelin and estradiol (injected via ICV route) on plasma T3 and T4 concentrations in female rats.Materials and Methods:Eighteen Wistar female rats (bodyweight, 200-250 g) were randomly divided into three groups. Group 1 received estradiol, Group 2 received ghrelin and Group 3 received ghrelin and estradiol. Plasma samples were used to assess T3 and T4 concentration by RIA.Results:The results indicated that ghrelin significantly decreased thyroid hormone concentrations, whereas estradiol increased these concentrations. The simultaneous injection of ghrelin and estradiol significantly decreased the inhibitory effect of ghrelin on thyroid hormone concentrations (P < 0.05).Conclusions:According to the results of this study, both ghrelin and estradiol affect the concentration of thyroid hormone but in opposite directions. This difference might be due to different underlying hormonal mechanisms such as HPA and/or HPT axis melanocyte stimulating hormone (MSH) systems could be suggested.

Growth hormone (GH)-releasing activity of chicken GH-releasing hormone (GHRH) in chickens

Two peptides with sequence similarities to growth hormone releasing hormone (GHRH) have been identified by analysis of the chicken genome. One of these peptides, chicken (c) GHRH-LP (like peptide) was previously found to poorly bind to chicken pituitary membranes or to cloned and expressed chicken GHRH receptors and had little, if any, growth hormone (GH)-releasing activity in vivo or in vitro. In contrast, a second more recently discovered peptide, cGHRH, does bind to cloned and expressed cGHRH receptors and increases cAMP activity in transfected cells. The possibility that this peptide may have in vivo GH-releasing activity was therefore assessed. The intravenous (i.v.) administration of cGHRH to immature chickens, at doses of 3–100μg/kg, significantly increased circulating GH concentrations within 10min of injection and the plasma GH levels remained elevated for at least 30min after the injection of maximally effective doses. The plasma GH responses to cGHRH were comparable with those induced by human (h) or porcine (p) GHRH preparations and to that induced by thyrotropin releasing hormone (TRH). In marked contrast, the i.v. injection of cGHRH-LP had no significant effect on circulating GH concentrations in immature chicks. GH release was also increased from slaughterhouse chicken pituitary glands perifused for 5min with cGHRH at doses of 0.1μg/ml or 1.0μg/ml, comparable with GH responses to hGHRH1–44. In contrast, the perifusion of chicken pituitary glands with cGHRH-LP had no significant effect on GH release. In summary, these results demonstrate that cGHRH has GH-releasing activity in chickens and support the possibility that it is the endogenous ligand of the cGHRH receptor.

The Levels of Ghrelin in Children with Cyanotic and Acyanotic Congenital Heart Disease

The cause of growth retardation in congenital heart disease is multifactorial. The relationship between congenital heart disease (CHD), malnutrition, and growth retardation is well documented. Ghrelin has effects on nutrient intake and growth. Ghrelin exerts potent GH-releasing activity and stimulates food intake. Circulating ghrelin levels are increased in anorexia and cachexia, reduced in obesity and restored by weight recovery. The relation between ghrelin and congenital heart disease is evident in adults but it is not studied well in pediatric age. The aim of the present study is to evaluate the serum ghrelin in congenital heart disease. We measured serum ghrelin, using ELISA technique in 60 patients with congenital heart disease (20 with acyanotic congenital heart disease with no heart failure (HF), 15 with cyanotic congenital heart disease with no HF) and 25 patients with congenital heart disease (cyanotic or acyanotic) with HF, in addition to 30 age and sex matched children as a control group. All children were subjected to measurement of height, weight, body mass index (BMI). In comparison to controls, serum ghrelin levels were significantly higher in patients with congenital heart disease (acyanotic patients and cyanotic with or without HF than in the control group (p=0.01). Also ghrelin level was significantly increased in children with cyanotic congenital heart disease than in those with acyanotic congenital heart disease. Patient with congenital heart disease with evidence of HF had significant higher levels of serum ghrelin than those with congenital heart disease without HF. Weight, height and BMI were significantly lower in cyanotic and acyanotic patients compared to the control group (p=0.001), also these measures were significantly reduced in patients with congenital heart disease with HF than in those without heart failure. There was a significant negative correlation between serum ghrelin and BMI in patients with heart failure, cyanotic patients and acyanotic patients; (r = -0.608, -0.831 and -0.458) and (p = 0.007, 0.02 and 0.017) respectively. In onclusion, serum ghrelin levels is elevated in children with acyanotic and cyanotic congenital heart disease with or without HF. Increased ghrelin levels represents malnutrition and growth retardation in these patients. This may suggest that ghrelin may have an important role as a compensatory mechanism in the regulation of the metabolic balance in these patients.

Epicardial Fat Thickness in Heart Failure and Other Clinical Conditions

In this issue of Angiology, Karayannis et al report that epicardial fat thickness (EFT) is related to anthropometric characteristics (body mass index [BMI], waist, or thigh perimeter) in both non-cachectic congestive heart failure (CHF) patients and controls. In addition, they found that in healthy individuals, decreased plasma ghrelin and increased high-sensitivity C-reactive protein (hsCRP) levels significantly predicted increased EFT, even after adjustment for BMI. On the other hand, the positive association of increased leptin with increased EFT in non-cachetic CHF was blunted after adjustment for BMI. Leptin is an adipocyte-derived protein hormone that is elevated in obesity and results in inhibition of food intake. Leptin causes energy consumption through central stimulation of sympathetic activation. Leptin appears to play multiple roles that include: functioning as a growth factor for various cell types, as a mediator of energy expenditure, as a permissive factor for puberty, and as a signal for modulation of fetal–maternal metabolism. Perhaps most importantly, leptin interacts with other hormonal mediators/regulators of energy metabolism such as insulin, glucagon, insulin-like growth factors, growth hormone (GH) and glucocorticoids. The complexity of the leptin axis suggests the unlikely development of simple obesity treatments. On the other hand, ghrelin is an appetite-stimulating peptide that is secreted by the stomach with regulation by food intake and it causes the release of GH. Ghrelin is released and circulates in the bloodstream under fasting conditions with transmission of a hunger signal to the central nervous system. As a peptide predominantly produced by the stomach and with strong GH-releasing activity, ghrelin contributes significantly to the regulation of diverse functions of the gut–brain axis. Therefore, ghrelin plays an important role in maintaining GH release and energy homeostasis in vertebrates. In patients with CHF, ghrelin has been shown to decrease plasma norepinephrine, increase left ventricular (LV) ejection fraction, increase LV mass, decrease LV endsystolic volume, decrease skeletal muscle wasting, and, during exercise, to increase peak workload plus peak oxygen consumption.

Pharmacological Characteristics of KP-102 (GHRP-2), a Potent Growth Hormone-Releasing Peptide

KP-102 (D-alanyl-3-(2-naphthyl)-D-alanyl-L-alanyl-L-tryptophyl-D-phenylalanyl-L-lysinamide dihydrochloride, growth hormone-releasing peptide-2, GHRP-2, pralmorelin, CAS 158861-67-7), is a potent synthetic growth hormone (GH) secretagogue. In the present study, the pharmacological characteristics of the GH-releasing property of KP-102 were investigated by means of in vivo and in vitro experiments. In conscious rats, the GH-releasing activity of KP-102 was more potent than that of exogenously injected GH-releasing hormone (GHRH). Under pentobarbital anesthesia in which endogenous somatostatin secretion is known to be decreased, KP-102 and GHRH, both showed an almost equivalent GH-releasing potency, which was also similar to that of KP-102 in conscious rats. Besides, KP-102 showed GH-releasing activity in conscious dogs as well, while GHRH failed to increase serum GH levels in conscious dogs. These findings suggest that the GH-releasing activity of KP-102 was less sensitive to GH suppression by endogenous somatostatin as compared with that of GHRH. The GH-releasing activity of KP-102 was completely absent in hypophysectomized rats, but present in median eminence-lesioned rats in which secreted GH amounts were significantly less than those normal rats, indicating necessity of the median eminence (endogenous GHRH) to exert the full activity of KP-102 in GH stimulation. KP-102 directly stimulated GH secretion from cultured rat anterior pituitary cells, although the GH-releasing potency of KP-102 was significantly weaker than that of GHRH in vitro. In conscious rats, KP-102 stimulated the secretion of both adrenocorticotrophic hormone (ACTH) and corticosterone, but not of prolactin. Three weeks administration of KP-102 showed growth-accelerating effect, a slight increase of body weight and wet weight of some organs in both normal and monosodium glutamate (MSG)-treated rats. These results suggest that KP-102 showed specific GH-releasing activity apart from slight ACTH secretion, and that the GH-releasing activity was stable in comparison with that of exogenously injected GHRH.

General Pharmacology of KP-102 (GHRP-2), a Potent Growth Hormone-Releasing Peptide

The general pharmacological effects of the hexapeptide KP-102 (D-alanyl-3-(2-naphthyl)-D-alanyl-L-alanyl-L-tryptophyl-D-phenylalanyl-L-lysinamide dihydrochloride, growth hormone-releasing peptide-2, GHRP-2, pralmorelin, CAS 158861-67-7), which potently promotes growth hormone (GH) release by acting at both hypothalamic and pituitary sites, were evaluated in various animal experimental models. The administration of KP-102 showed no obvious effect at a pharmacological dose on the central nervous system. KP-102 had no significant effect on the autonomic nervous system and smooth muscle except a slight and transient increase in spontaneous motility of isolated rabbit ileum and contraction of isolated guinea pig ileum at high doses. There was negligible effect on the respiratory and cardiovascular systems, digestive system, renal function and blood system after KP-102 treatment. These results suggest that KP-102 has no serious general pharmacological effects at dose levels showing GH-releasing activity in the experimental animals. Therefore, it is concluded that KP-102 will be a useful drug for the diagnosis of serious GH deficiency and for treatment of short stature.

The Glucagon Test in the Diagnosis of Growth Hormone Deficiency in Children With Short Stature Younger than 6 Years

Few studies have addressed the diagnostic role of the glucagon test in children with suspected GH deficiency (GHD). The objective of the study was to investigate the diagnostic value of the glucagon test as an alternative test to insulin tolerance test (ITT) and arginine in GHD children younger than 6 yr. This study was conducted in two pediatric endocrinology centers. Forty-eight children (median age 4.2 yr, median height -3.0 sd score) with GHD confirmed by a peak GH to ITT and arginine less than 10 microg/liter (median 4.7 and 3.4 microg/liter, respectively) underwent a glucagon stimulation test. Magnetic resonance imaging showed normal hypothalamic-pituitary anatomy in 24 children, isolated anterior pituitary hypoplasia in seven, and structural hypothalamic-pituitary abnormalities in 17. Median GH peak response to glucagon (13.5 microg/liter) was significantly higher than that observed after ITT and arginine (P < 0.0001). GH peak after glucagon was less than 10 microg/liter in 20 subjects (group 1) and greater than 10 microg/liter in 28 subjects (group 2) without significant clinical or biochemical differences between the two groups. Median GH peak after glucagon was similar between patients with multiple pituitary hormone deficiency and those with isolated GHD and between subjects with and without structural hypothalamic-pituitary abnormalities. The magnitude of the GH peak after glucagon was negatively correlated to age at diagnosis (rho = -0.636, P < 0.0001). This study shows that glucagon has an effective GH-releasing activity and can be used to evaluate somatotroph function in young children with short stature. Normative data for this test in young children need to be established before its use in clinical practice.

Ghrelin and Growth Hormone Secretagogues, Physiological and Pharmacological Aspect

The first "growth hormone secretagogues" (GHSs) were discovered by Bowers et al. in 1977. In 1996 the GHSs receptor (GHS-R 1a) was cloned. The endogenous ligand for this receptor, ghrelin, was not identified until 1999. Synthetic molecules termed GHSs are substances that stimulate growth hormone (GH) release, via a separate pathway distinct from GH releasing hormone (GHRH)/somatostatin. Ghrelin displays strong GH-releasing activity through the activation of the GHS-R 1a. Apart from stimulating GH secretion, ghrelin and many synthetic GHSs: 1) stimulate prolactin and ACTH secretion; 2) negatively influence the pituitary-gonadal axis; 3) stimulate appetite and positive energy balance; 4) modulate pancreatic endocrine function and affect glucose levels; 5) have cardiovascular actions. The control of ghrelin secretion is not well established at present, although nutrition is an important regulator. Investigators have exploited the ability of GHSs and ghrelin to release GH by mechanisms different from GHRH as a diagnostic tool, which is the present main clinical use of some GHSs. As an alternative to GH, GH deficient conditions could be treated with any substance which would release endogenous GH, such as synthetic GHSs. It is likely that GHSs, acting as either agonists or antagonists on different pathophysiological processes, might have some other clinical impact and therapeutic potential. At least theoretically ghrelin receptor antagonists could be anti-obesity drugs, as blockers of the orexigenic signal from the gastrointestinal tract to the brain. Inverse agonists of the ghrelin receptor, by blocking the constitutive receptor activity, might lower the set-point for hunger between meals.

Acute ghrelin response to intravenous dexamethasone administration in idiopathic short stature or isolated idiopathic growth hormone-deficient children

Acylated ghrelin has been originally described for its potent GH-releasing activity mediated by the activation of the GH secretagogue receptor type 1a. More recently, ghrelin has been reported to exert several other GH-independent biological actions, among which in the modulation of metabolic functions. Glucocorticoids are well known to exert important metabolic functions but also to modulate GH secretion, although through mechanisms that have not been fully clarified so far. Interestingly, the existence of a feedback link between glucocorticoids and ghrelin system has already been reported. The aim of our study was to evaluate the acute GH and ghrelin responses to dexamethasone (DEX) administration in children with idiopathic short stature (ISS) or isolated idiopathic GH deficiency (GHD). Eight children with ISS (age: 9.5+/-1.2 yr) and 7 with GHD (12.1+/-1.4 yr) underwent iv DEX administration (0.3 mg/body surface area at 0 min). IGF-I, GH, and ghrelin levels were assayed at baseline and every 30 min from 120 up to 240 min after DEX. Compared to baseline levels DEX decreased ghrelin in ISS at 120 min and 240 min (p<0.04). On the other hand DEX did not modify ghrelin levels in GHD. After DEX, ghrelin was reduced in ISS compared to GHD (p<0.02). DEX increased GH in ISS but not in GHD (peak: 11.1+/-1.2 vs 7.6+/-0.9 microg/l). Basal, as well as after-DEX ghrelin levels negatively correlated with IGF-I in GHD (p<0.03) and with height SD score (HSDS) in ISS (p<0.02). Acute DEX administration is able to decrease ghrelin in ISS, but not in GHD children. Both basal and after-DEX ghrelin levels negatively correlate with IGF-I and HSDS. All these data suggest the existence of a feedback link among ghrelin, glucocorticoids and the GH/IGF-I axis.

Effects of ghrelin administration on endocrine and metabolic parameters in obese women with polycystic ovary syndrome

The novel peptide ghrelin displays multiple endocrine and non-endocrine actions. Its strong GH-releasing activity in humans has long been recognized. However, in obesity, ghrelin administration induces a blunted GH secretion, enhances glucose and reduces insulin levels. The effects of ghrelin administration have not been investigated in polycystic ovary syndrome (PCOS), which can be associated with obesity, hyperinsulinism, and GH hyposecretion. Leptin is a mediator for energy balance opposed to ghrelin; both of them are supposed to act as regulators of reproductive functions. Evaluate the endocrine and metabolic response to ghrelin administration in PCOS obese patients compared to body mass index (BMI)-matched and normal weight women. Nine obese PCOS patients (BMI: 35.4+/-1.2 kg/m(2)) (OB PCOS), 6 obese controls (BMI: 38.4+/-1.1 kg/m(2)) (Ob), and 6 normal-weight women (BMI: 23+/-0.6 kg/m(2)) (NW) were enrolled in the study. In all patients we performed: 1) basal hormonal evaluation including FSH, LH, estradiol, testosterone, androstenedione, DHEAS, SHBG, 17-hydroxyprogesterone (17OHP), IGF-I, free T3 (FT3), free T4 (FT4) and ghrelin levels; 2) metabolic evaluation as follows: concentration of non-esterified fatty acid (NEFA) and oral glucose tolerance test (OGTT) (75 g); homeostasis model assessment (HOMA); glucose and insulin response to ghrelin administration (1 microg/kg); 3) measurement of GH, PRL, TSH, and leptin levels after infusion of ghrelin. Administration of ghrelin increased glucose and reduced insulin levels in both Ob and OB PCOS. Moreover, ghrelin enhanced GH and PRL levels in all groups but it did not modify TSH and leptin levels. GH peak and area under the curve (AUC) in OB PCOS and Ob were lower than controls (p<0.05). Similar PRL peak and AUC values were observed in all groups. In both obese and PCOS obese patients, leptin levels are not influenced by ghrelin administration. Moreover, the GH response after ghrelin administration is blunted. However, ghrelin exerts glucose- enhancing and insulin-lowering effects, the latter absent in NW.

Discovery of growth hormone-releasing hormones and receptors in nonmammalian vertebrates

In mammals, growth hormone-releasing hormone (GHRH) is the most important neuroendocrine factor that stimulates the release of growth hormone (GH) from the anterior pituitary. In nonmammalian vertebrates, however, the previously named GHRH-like peptides were unable to demonstrate robust GH-releasing activities. In this article, we provide evidence that these GHRH-like peptides are homologues of mammalian PACAP-related peptides (PRP). Instead, GHRH peptides encoded in cDNAs isolated from goldfish, zebrafish, and African clawed frog were identified. Moreover, receptors specific for these GHRHs were characterized from goldfish and zebrafish. These GHRHs and GHRH receptors (GHRH-Rs) are phylogenetically and structurally more similar to their mammalian counterparts than the previously named GHRH-like peptides and GHRH-like receptors. Information regarding their chromosomal locations and organization of neighboring genes confirmed that they share the same origins as the mammalian genes. Functionally, the goldfish GHRH dose-dependently activates cAMP production in receptor-transfected CHO cells as well as GH release from goldfish pituitary cells. Tissue distribution studies showed that the goldfish GHRH is expressed almost exclusively in the brain, whereas the goldfish GHRH-R is actively expressed in brain and pituitary. Taken together, these results provide evidence for a previously uncharacterized GHRH-GHRH-R axis in nonmammalian vertebrates. Based on these data, a comprehensive evolutionary scheme for GHRH, PRP-PACAP, and PHI-VIP genes in relation to three rounds of genome duplication early on in vertebrate evolution is proposed. These GHRHs, also found in flounder, Fugu, medaka, stickleback, Tetraodon, and rainbow trout, provide research directions regarding the neuroendocrine control of growth in vertebrates.

Pharmacokinetics and Pharmacodynamic Effects of an Oral Ghrelin Agonist in Healthy Subjects

An oral formulation of EP01572, a peptidomimetic growth hormone secretagogue, was studied. An oral delivery system would be preferable in many of the possible therapeutic indications of ghrelin agonists such as EP01572. Our objective was to establish the pharmacological profile and the GH-releasing activity of increasing oral doses of EP01572 in healthy volunteers. In addition, the pharmacokinetics and pharmacological effects of EP01572 were investigated after intraduodenal (ID) administration. This study was a single-center escalating dose study with oral and ID applications. In the first part, EP01572 was given orally to 36 male subjects; the treatment consisted of one oral dose of either EP01572 or placebo (0.005, 0.05, and 0.5 mg/kg body weight). Six subjects received two additional oral doses of EP01572: 0.125 and 0.25 mg/kg body weight. In the second part, the following treatments were performed in a randomized order: 1) administration of a bolus of saline (placebo) to the small intestine; 2) ID administration of a bolus of EP01572 at 0.2 mg/kg body weight; 3) ID perfusion of a bolus of EP01572 at 0.35 mg/kg body weight; and 4) ID perfusion of a bolus of EP01572 at 0.5 mg/kg body weight. The oral and ID administration of EP01572 induced a rapid and dose-dependent increase in plasma drug concentrations and a potent GH release in healthy male volunteers. This study showed that EP01572 was active with regard to stimulation of GH release in humans after oral and ID administration.

Administration of exogenous ghrelin in obese patients with polycystic ovary syndrome: effects on plasma levels of growth hormone, glucose, and insulin

To assess the effects of the administration of exogenous ghrelin, a peptide with potent GH-releasing activity and glucose-enhancing and insulin-lowering properties, in obese patients with polycystic ovary syndrome (PCOS). Prospective, controlled study. Academic research environment. Twenty obese women with PCOS, and 15 obese controls. Oral glucose tolerance test (OGTT) and ghrelin test (1 microg/kg i.v. bolus). Basal hormonal assays, including ghrelin, were performed. Glucose, insulin, and C-peptide were assessed in a fasting condition and during the OGTT. Growth hormone, insulin, and glucose were measured basally and every 15 minutes for 90 minutes after the injection of ghrelin. Both groups showed an insulin response to the glucose load above the normal range. Significantly lower levels of ghrelin were detected in patients with PCOS compared to controls (108.96 +/- 27.65 Fmol/mL versus 162.47 +/- 42.23 Fmol/mL). Administration of ghrelin markedly enhanced GH levels in both groups (1,888.59 +/- 1,209.53 ng/mL and 1,639.95 +/- 631.79 ng/mL per 90 minutes as GH area under the curve, respectively), with a peak occurring 30 minutes after injection. Ghrelin also induced a trend toward an increase in plasma glucose levels, and a significant decrease in insulin concentrations in both groups. The injection of ghrelin seems to override the GH secretion defect in obese women with PCOS, and to induce glucoinsulinemic changes in both controls and obese patients with PCOS.

A Novel hGHRH Analog and its Comparative Activity

Growth hormone releasing hormone is one of the hormones secreted from the hypothalamus. Because of its potential applications in agriculture and medicine, its short half-life and its expensive chemical synthesis, an analog with high GHRH activity and prolonged half-life was sought after. The fusion partner gene with 127 amino acid residues of the C-terminus from L-asparaginase was recombined with asp-pro-hGHRH(1-44) gene synthesized by PCR method to form one kind of fusion protein with unique acid labile linker Asp-Pro. The Pro-hGHRH(1-44) peptide was purified to homogeneity by means of cell disruption, washing, ethanol precipitation, acid hydrolysis, SP-Sephadex C-25, and Sephadex G-10 column chromatography. The peptide's molecular weight of 5,139 Da as measured by EIS-MS was coincident with the actual values. In the study of the activity, the doses of peptide were 0.1, 1.0, and 10 microg/ml for rat pituitary and 5 microg/ml for human pituitary. The peptide increased GH releases from rat pituitary in a concentration-dependent manner (P<0.05; P<0.01). At 1.0 microg/ml, there was a significant difference between Pro-Pro-hGHRH(1-44)-Gly-Gly-Cys and Pro-hGHRH(1-44) or Pro-Pro-hGHRH(1-44) (P<0.05), whereas the standard hGHRH(1-40) showed no measured rGH release. For human fetal pituitary, the Pro-hGHRH(1-44) peptides showed good GH-releasing activity, but there were no significant differences between them. The structure-activity relationship showed that for both rat and human fetal pituitary, the net GH-releasing activity of the Pro-hGHRH(1-44) analog was more than that of Pro-Pro-hGHRH(1-44). The results of the other hormones from human pituitary showed that the analog had good function-selectivity and species specificity.

Drug Insight: the functions of ghrelin and its potential as a multitherapeutic hormone

The endogenous ligand for the growth-hormone (GH) secretagogue receptor was purified from stomach and named ghrelin. It has potent GH-releasing activity and stimulates appetite by acting on the hypothalamic arcuate nucleus, a region known to control food intake. Ghrelin thus plays important roles in maintaining GH release and energy homeostasis in vertebrates. Ghrelin, moreover, stimulates gastric motility and acid secretion, shows positive cardiovascular effects, and has direct actions on bone formation. The diverse functions of ghrelin raise the possibility of its clinical application for GH deficiency, eating disorders, gastrointestinal disease, cardiovascular disease, osteoporosis and aging.

Ghrelin, an endogenous growth hormone secretagogue with diverse endocrine and nonendocrine effects

Circulating ghrelin, the natural ligand of GHS-R 1a, is synthesized primarily in the stomach in mammals. The distribution of these receptors is consistent with the role of ghrelin in promoting secretion of GH; receptors are highly expressed in the hypothalamus and pituitary gland and are also distributed in other central and peripheral tissue sites. In addition to strong GH-releasing activity, ghrelin has other actions, including stimulation of lactotroph and corticotroph function, stimulation of appetite, regulation of energy homeostasis, stimulation of gastric motility and gastric acid secretion, regulation of insulin secretion and glucose metabolism, cardiovascular effects, and antiproliferative activity. These properties make ghrelin a candidate for future diagnostic and clinical applications. In mammals, secretion of GH from the adenohypophysis is regulated by 2 hypothalamic hormones with antagonistic actions: a stimulatory GHRH that is produced in the arcuate nucleus and an inhibitory hormone, somatostatin, synthesized in the paraventricular nucleus. 1 Both hormones are transported from the hypothalamus to target cells in the pituitary gland via the hypothalamo-hypophyseal portal system in the median eminence. Alternation in secretion of GHRH and somatostatin is responsible for the pulsatile pattern of GH release. 2,3 Measurement of GHRH and somatostatin in hypophyseal-portal blood in humans and other animals reveals that the episodic pattern of GHRH and somatostatin secretion does not fully account for all pulses of GH secretion. 4 The amplitude and frequency of GH secretory pulses are regulated by a complex array of external and internal stimuli, including body composition, age, sleep, gender, disease status, menstrual cycle phase, genetic background, and nutritional status. 5–7