http://repub.eur.nl/res/aut/7432/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/29370/ 2008-02-01T00:00:00Z Cortistatin (CST), a neuropeptide with high structural homology with somatostatin (SST), binds all SST receptor (SST-R) subtypes but, unlike SST, also shows high binding affinity to ghrelin receptor (GHS-R1a). CST exerts the same endocrine activities of SST in humans, suggesting that the activation of the SST-R might mask the potential interaction with ghrelin system. CST-8, a synthetic CST-analogue devoid of any binding affinity to SST-R but capable to bind the GHS-R1a, has been reported able to exert antagonistic effects on ghrelin actions either in vitro or in vivo in animals. We studied the effects of CST-8 (2.0 μg/kg iv as a bolus or 2.0 μg/kg/h iv as infusion) on both spontaneous and ghrelin- or hexarelin- (1.0 μg/kg iv as bolus) stimulated GH, PRL, ACTH and cortisol secretion in 6 normal volunteers. During saline, no change occurred in GH and PRL levels while a spontaneous ACTH and cortisol decrease was observed. As expected, both ghrelin and hexarelin stimulated GH, PRL, ACTH and cortisol secretion (p < 0.05). CST-8, administered either as bolus or as continuous infusion, did not modify both spontaneous and ghrelin- or hexarelin-stimulated GH, PRL, ACTH and cortisol secretion. In conclusion, CST-8 seems devoid of any modulatory action on either spontaneous or ghrelin-stimulated somatotroph, lactotroph and corticotroph secretion in humans in vivo. These negative results do not per se exclude that, even at these doses, CST-8 might have some neuroendocrine effects after prolonged treatment or that, at higher doses, may be able to effectively antagonize ghrelin action in humans. However, these data strongly suggest that CST-8 is not a promising candidate as GHS-R1a antagonist for human studies to explore the functional interaction between ghrelin and cortistatin systems. http://repub.eur.nl/res/pub/35854/ 2007-02-01T00:00:00Z Acylated ghrelin exerts numerous endocrine and non-endocrine activities via the GH Secretagogue receptor type 1a (GHS-R1a). d-Lys-GHRP-6 has been widely studied in vitro and in vivo in animal studies as GHS-R1a antagonist; its action in humans has, however, never been tested so far. Aim of our study was to verify the antagonistic action of d-Lys-GHRP-6 on the endocrine responses to acylated ghrelin and hexarelin, a peptidyl synthetic GHS, in humans. The effects of different doses of d-Lys-GHRP-6 (2.0 μg/kg iv as bolus or 2.0 μg/kg/h iv as infusion) on both spontaneous and acylated ghrelin- or hexarelin (1.0 μg/kg iv as bolus) -stimulated GH, PRL, ACTH and cortisol levels were studied in six normal volunteers (age [mean ± SEM]: 25.4 ± 1.2 yr; BMI: 22.3 ± 1.0 kg/m2). The effects of d-Lys-GHRP-6 (2.0 μg/kg iv as bolus + 4.0 μg/kg/h iv) on the GH response to 0.25 μg/kg iv as bolus acylated ghrelin was also studied. During saline, spontaneous ACTH and cortisol decrease was observed while non changes occurred in GH and PRL levels. Acylated ghrelin and hexarelin stimulated (p < 0.05) GH, PRL, ACTH and cortisol secretions. d-Lys-GHRP-6 administered either as bolus or a continuous infusion did not modify both spontaneous and acylated ghrelin- or hexarelin-stimulated GH, PRL, ACTH and cortisol secretion. d-Lys-GHRP-6 did not modify even the GH response to 0.25 μg/kg iv acylated ghrelin. In conclusion, d-Lys-GHRP-6 does not affect the neuroendocrine response to both ghrelin and hexarelin. These findings question d-Lys-GHRP-6 as an effective GHS-R1a antagonist for human studies. http://repub.eur.nl/res/pub/13570/ 2005-02-01T00:00:00Z Ghrelin exerts various metabolic activities, including regulation of glucose levels in humans. To verify whether the glucose response to ghrelin reflects a modulation of an insulin-independent hepatic phenomenon, we studied glucose output by primary porcine hepatocytes in suspension culture, after incubation with acylated ghrelin (AG), unacylated ghrelin (UAG), and hexarelin (HEX). AG induced glucose output dose dependently after 20 min of incubation (P < 0.001), whereas HEX, a GH secretagogue receptor type 1a (GHS-R1a) agonist, had no effect. UAG inhibited glucose release also dose dependently and after 20 min (P < 0.001). Moreover, UAG completely reversed AG-induced glucose output (P < 0.01). Using real-time PCR, GHS-R1a gene expression was undetectable in all the hepatocyte preparations studied. The lack of efficacy of HEX, the efficacy of UAG, and the absence of GHS-R1a expression indicate the involvement of a yet uncharacterized ghrelin receptor type. In conclusion, glucose output by primary hepatocytes is time- and dose-dependently stimulated by AG and inhibited by UAG. Moreover, UAG counteracts the stimulatory effect of AG on glucose release. These actions might be mediated by a different receptor than GHS-R1a, and apparently, we must consider AG and UAG as separate hormones that can modify each other's actions on glucose handling, at least in the liver. http://repub.eur.nl/res/pub/13514/ 2004-10-01T00:00:00Z We investigated the metabolic actions of ghrelin in humans by examining the effects of acute administration of acylated ghrelin, unacylated ghrelin, and the combination in eight adult-onset GH-deficient patients. We followed glucose, insulin, and free fatty acid concentrations before and after lunch and with or without the presence of GH in the circulation.We found that acylated ghrelin, which is rapidly cleared from the circulation, induced a rapid rise in glucose and insulin levels. Unacylated ghrelin, however, prevented the acylated ghrelin-induced rise in insulin and glucose when it was coadministered with acylated ghrelin. Surprisingly, the injection of acylated ghrelin induced an acute increase in unacylated ghrelin and therefore total ghrelin levels. Finally, acylated ghrelin decreased insulin sensitivity up to the end of a period of 6 h after administration. This decrease in insulin sensitivity was prevented by coinjection of unacylated ghrelin. This combined administration of acylated and unacylated ghrelin even significantly improved insulin sensitivity, compared with placebo, for at least 6 h, which warrants studies to investigate the long-term efficacy of this combination in the treatment of disorders with disturbed insulin sensitivity. http://repub.eur.nl/res/pub/13418/ 2004-06-01T00:00:00Z Ghrelin possesses strong GH-releasing activity but also other endocrine activities including stimulation of PRL and ACTH secretion, modulation of insulin secretion and glucose metabolism. It is assumed that the GH secretagogue (GHS) receptor (GHS-R) 1a mediates ghrelin actins provided its acylation in Serine 3; in fact, acylated ghrelin only is able to exert endocrine activities. Acylated ghrelin (AG) is present in serum at a 2.5 fold lower concentration than unacylated ghrelin (UAG). UAG, however, is not biologically inactive; it shares with AG some non-endocrine actions like cardiovascular effects, modulation of cell proliferation and even some influence on adipogenesis. Thus, these actions are likely to be mediated by GHS-R subtypes able to bind ghrelin independently of its acylation. In order to further clarify whether UAG is really devoid of any endocrine action, we studied the interaction of the combined administration of AG and UAG (1.0 microg/kg i.v.) in 6 normal young volunteers (age [mean +/- SE]: 25.4 +/- 1.2 yr; BMI: 22.3 +/- 1.0 kg/m2). As expected, AG induced marked increase (p < 0.01) in circulating GH, PRL, ACTH and cortisol levels. AG administration was also followed by a decrease in insulin levels (-285.4 +/- 64.8 mU*min/l; p < 0.05) and an increase in plasma glucose levels (1068.4 +/- 390.4 mg*min/dl; p < 0.01). UAG alone did not induce any change in these parameters. UAG also failed to modify the GH, PRL, ACTH and cortisol responses to AG. However, when UAG was co-administered together with AG, no significant change in insulin (-0.5 +/- 40.9 mU*min/l) and glucose levels (455.9 +/- 88.3 mg*min/dl) was recorded anymore, indicating that the insulin and glucose response to AG has been abolished by UAG. In conclusion, non-acylated ghrelin does not affect the GH, PRL, and ACTH response to acylated ghrelin but is able to antagonize the effects of acylated ghrelin on insulin secretion and glucose levels. These findings indicate that unacylated ghrelin is metabolically active and is likely to counterbalance the influence of acylated ghrelin on insulin secretion and glucose metabolism. As GHS-R1a is not bound by unacylated ghrelin, these findings suggest that GHS receptor subtypes mediate the metabolic actions of both acylated and unacylated ghrelin. http://repub.eur.nl/res/pub/10339/ 2004-01-01T00:00:00Z Ghrelin secretion has been reportedly increased by fasting and energy restriction but decreased by food intake, glucose, insulin, and somatostatin. However, its regulation is still far from clarified. The cholinergic system mediates some ghrelin actions, e.g. stimulation of gastric contractility and acid secretion and its orexigenic activity. To clarify whether ghrelin secretion undergoes cholinergic control in humans, we studied the effects of pirenzepine [PZ, 100 mg per os (by mouth)], a muscarinic antagonist, or pyridostigmine (PD, 120 mg per os), an indirect cholinergic agonist, on ghrelin, GH, insulin, and glucose levels in six normal subjects. PD increased (P < 0.05) GH (change in area under curves, mean +/- SEM, 790.9 +/- 229.3 microg(*)min/liter) but did not modify insulin and glucose levels. PZ did not significantly modify GH, insulin, and glucose levels. Circulating ghrelin levels were increased by PD (11290.5 +/- 6688.7 pg(*)min/ml; P < 0.05) and reduced by PZ (-23205.0 +/- 8959.5 pg(*)min/ml; P < 0.01). The PD-induced ghrelin peak did not precede that of GH. In conclusion, circulating ghrelin levels in humans are increased and reduced by cholinergic agonists and antagonists, respectively. Thus, ghrelin secretion is under cholinergic, namely muscarinic, control in humans. The variations in circulating ghrelin levels induced by PD and PZ are unlikely to mediate the cholinergic influence on GH secretion. http://repub.eur.nl/res/pub/31815/ 2003-09-01T00:00:00Z Ghrelin possesses central and peripheral endocrine actions including influence on the endocrine pancreatic function. To clarify this latter ghrelin action, in seven normal young subjects [age (mean ± SEM), 28.3 ± 3.1 yr; body mass index, 21.9 ± 0.9 kg/m2), we studied insulin and glucose levels after acute ghrelin administration (1.0 μg/kg iv) alone or combined with glucose [oral glucose tolerance test (OGTT), 100 g orally], arginine (ARG, 0.5 g/kg iv) or free fatty acid (FFA, Intralipid 10%, 250 ml). Ghrelin inhibited (P < 0.05) insulin and increased (P < 0.05) glucose levels. OGTT increased (P < 0.01) glucose and insulin levels. FFA increased (P < 0.05) glucose but did not modify insulin levels. ARG increased (P < 0.05) both insulin and glucose levels. Ghrelin did not modify both glucose and insulin responses to OGTT as well as the FFA-induced increase in glucose levels; however, ghrelin administration was followed by transient insulin decrease also during FFA. Ghrelin blunted (P < 0.05) the insulin response to ARG and enhanced (P < 0.05) the ARG-induced increase in glucose levels. In all, ghrelin induces transient decrease of spontaneous insulin secretion and selectively blunts the insulin response to ARG but not to oral glucose load. On the other hand, ghrelin raises basal glucose levels and enhances the hyperglycemic effect of ARG but not that of OGTT. These findings support the hypothesis that ghrelin exerts modulatory action of insulin secretion and glucose metabolism in humans. http://repub.eur.nl/res/pub/9941/ 2002-01-01T00:00:00Z INTRODUCTION: In an animal model of acromegaly (PEPCK-hGH transgenic mice), low systemic levels of ghrelin have been observed compared with normal mice. We hypothesized that systemic circulating ghrelin levels are also decreased in humans with active acromegaly and that the contribution of central ghrelin production to systemic ghrelin levels is minimal. OBJECTIVES: The aim of the present study was to investigate, in two subjects with active acromegaly, whether there are differences between systemic ghrelin levels and ghrelin concentrations in the petrosal sinus. DESIGN: We measured systemic and central ghrelin levels in these two acromegalic patients by bilateral simultaneous inferior petrosal sinus sampling. Central and systemic blood samples were drawn before and 1, 5, 10, 15 and 20 min after stimulation with GH-releasing hormone (GHRH). Ghrelin was measured with a commercially available radioimmunoassay. RESULTS: In one acromegalic subject, the baseline systemic and central ghrelin levels were within the same range as in two non-acromegalic obese subjects. No gradient could be observed between central and systemic ghrelin concentrations. Stimulation with GHRH did not change the ghrelin concentrations in this patient. In the other acromegalic subject, the systemic ghrelin levels were also in the same range as in two non-acromegalic obese subjects. However, in this subject, baseline ghrelin concentrations in the right inferior petrosal vein were considerably lower than the systemic ghrelin concentrations, indicating a peripheral over central gradient. Administration of GHRH induced a significant rise in central ghrelin concentrations in the right inferior petrosal vein. Ghrelin levels in the left inferior petrosal vein and systemic ghrelin levels were in the normal range and GHRH stimulation did not change these concentrations. CONCLUSIONS: The absence of a central over peripheral ghrelin gradient in these two acromegalics indicated that circulating ghrelin is mainly produced peripherally. Circulating systemic ghrelin levels were not decreased in these two subjects with active acromegaly.