Andrea Benso

Non-acylated ghrelin does not possess the pituitaric and pancreatic endocrine activity of acylated ghrelin in humans

Ghrelin, a 28-amino acid peptide predominantly produced by the stomach, displays strong GH-releasing activity mediated by the GH secretagogue (GHS)-receptor (GHS-R) type 1a at the hypothalamus-pituitary level. Ghrelin and synthetic GHS also possess other GH-independent peripheral endocrine and non-endocrine activities via the activation of peripheral GHS-R subtypes. In rats in vivo non-acylated ghrelin has been reported devoid of any endocrine activity; however, in vitro, it has been shown as effective as ghrelin in exerting anti-proliferative activity on tumor cell lines. The aim of the present study was to clarify whether non-acylated human ghrelin shares some of the endocrine activities of its acylated form in humans. To this goal, the effects of acylated or non-acylated ghrelin (1.0 μg/kg iv at 0 min) on GH, PRL, ACTH, F, insulin and glucose levels were studied in two different testing sessions in 7 normal young volunteers (age [mean±SE]: 24.3±1.7 yr; BMI: 21.5±0.9 kg/m2). The effects of placebo administration were also studied. The administration of acylated ghrelin induced prompt and marked increase in circulating GH levels (AUC: 5452.4±904.9 μg*min/l; p<0.01 vs placebo) and significant increase in PRL (1273.5±199.7 μg*min/l; p<0.01 vs placebo), ACTH (4482.7±954.4 pg*min/ml; p<0.01 vs placebo) and F levels (15985.0±1141.9 μg*min/l; p<0.01 vs placebo). Its administration was also followed by decrease in insulin levels (1448.67±137.9 mU*min/l; p<0.05 vs placebo) that was coupled with an increase in plasma glucose levels (10974.2±852.5 mg*min/dl; p<0.05 vs placebo). The administration of non-acylated ghrelin and that of placebo did not induce any change in the hormonal parameters or in glucose levels. In conclusion, this study shows that in humans nonacylated ghrelin does not possess the pituitaric and pancreatic endocrine activities of human ghrelin octanoylated in Serine 3.

The GH-releasing effect of ghrelin, a natural GH secretagogue, is only blunted by the infusion of exogenous somatostatin in humans.

objective Ghrelin, a 28‐amino‐acid peptide purified from the stomach and showing a unique structure with an n‐octanoyl ester at the serine 3 residue, is a natural ligand of the GH secretagogue (GHS) receptor (GHS‐R). Ghrelin strongly stimulates GH secretion in both animals and humans, showing a synergistic effect with GH‐releasing hormone (GHRH) but no interaction with synthetic GHS. However, the activity of ghrelin as well as that of non‐natural GHS is not fully specific for GH; ghrelin also induces a stimulatory effect on lactotroph and corticotroph secretion, at least in humans.

Endocrine and metabolic responses to extreme altitude and physical exercise in climbers

CONTEXT Chronic hypoxia induces complex metabolic and endocrine adaptations. High-altitude (HA) exposure is a physiological model of hypoxia. OBJECTIVE To further investigate the endocrine and metabolic responses to extreme HA. METHODS We studied nine male elite climbers at sea level and at 5200 m after climbing Mt. Everest. RESULTS After 7 weeks at HA, body weight was reduced (P<0.05); regarding endocrine variables we observed: a) an increase of 2-h mean GH concentration (P<0.05) as well as of total IGF-I and IGF binding protein-3 levels (P<0.05 for both); b) a prolactin increase (P<0.05) coupled with testosterone decrease (P<0.01) and progesterone increase (P<0.05) without any change in estradiol levels: c) no change in cortisol, ACTH, and dehydroepiandrosterone sulfate (DHEAS) levels; d) an increase in free thyroxine (P<0.05) and free tri-iodothyronine (T(3)) decrease (P<0.05) but no change in TSH levels; e) a plasma glucose decrease (P<0.05) without any change in insulin levels; f) an increase in mean free fatty acid levels (P<0.05); g) despite body weight loss, leptin levels showed non-significant trend toward decrease, while ghrelin levels did not change at all. CONCLUSIONS The results of the present study in a unique experimental human model of maximal exposure to altitude and physical exercise demonstrate that extreme HA and strenuous physical exercise are coupled with specific endocrine adaptations. These include increased activity of the GH/IGF-I axis and a low T(3) syndrome but no change in ghrelin and leptin that was expected taking into account body weight decrease. These findings would contribute to better understanding human endocrine and metabolic physiology in hypoxic conditions.

Effects of glucose, free fatty acids or arginine load on the GH-releasing activity of ghrelin in humans

objective Ghrelin, a 28 amino acid peptide purified from the stomach and showing a unique structure with an n‐octanoyl ester in serine‐3 residue, is a natural ligand of the GH secretagogue (GHS) receptor (GHS‐R) and strongly stimulates GH secretion. In humans, ghrelin is more potent than growth hormone‐releasing hormone (GHRH) and non‐natural GHS such as hexarelin. Moreover, ghrelin shows a true synergism with GHRH, has no interaction with hexarelin and, similarly to non‐natural GHS, is partially refractory to the inhibitory effect of exogenous somatostatin (SS). Despite this evidence, the mechanisms underlying the GH‐releasing effect of ghrelin in humans have not been fully clarified.

Metabolic effects of overnight continuous infusion of unacylated ghrelin in humans

OBJECTIVE To clarify the metabolic effects of an overnight i.v. infusion of unacylated ghrelin (UAG) in humans. UAG exerts relevant metabolic actions, likely mediated by a still unknown ghrelin receptor subtype, including effects on β-cell viability and function, insulin secretion and sensitivity, and glucose and lipid metabolism. DESIGN We studied the effects of a 16-h infusion (from 2100 to 1300  h) of UAG (1.0  μg/kg per h) or saline in eight normal subjects (age (mean±s.e.m.), 29.6±2.4 years; body mass index (BMI), 22.4±1.7  kg/m(2)), who were served, at 2100 and 0800  h respectively, with isocaloric balanced dinner and breakfast. Glucose, insulin, and free fatty acid (FFA) levels were measured every 20  min. RESULTS In comparison with saline, UAG induced significant (P<0.05) changes in glucose, insulin, and FFA profiles. UAG infusion decreased glucose area under the curve (AUC) values by 10% (UAG(0 - 960  min): 79.0±1.7×10(3)  mg/dl per min vs saline(0- 960  min): 87.5±3.8×10(3)  mg/dl per min) and the AUC at night by 14% (UAG(180)(-)(660  min): 28.4±0.5×10(3)  mg/dl per min vs saline(180 - 660  min): 33.2±1.1×10(3)  mg/dl per min). The overall insulin AUC was not significantly modified by UAG infusion; however, insulin AUC observed after meals was significantly increased under the exposure to UAG with respect to saline at either dinner or breakfast. The FFA AUC values were decreased by 52% under the exposure to UAG in comparison with saline (UAG(0 - 960  min): 0.3±0.02×10(3)  mEq/l per min vs saline(0 - 960  min): 0.6±0.05×10(3)  mEq/l per min). CONCLUSIONS Exposure to the i.v. administration of UAG improves glucose metabolism and inhibits lipolysis in healthy volunteers. Thus, in contrast to the diabetogenic action of AG, UAG displays hypoglycemic properties.

Ghrelin and the endocrine pancreas.

Ghrelin is a 28-amino-acid peptide predominantly produced by the stomach, while substantially lower amounts derive from other tissues including the pancreas. It is a natural ligand of the GH secretagogue (GHS) receptor (GHS-R1a) and strongly stimulates GH secretion, but acylation in serine 3 is needed for its activity. Ghrelin also possesses other endocrine and nonendocrine actions reflecting central and peripheral GHS-R distribution including the pancreas. The wide spectrum of ghrelin activities includes orexigenic effect, control of energy expenditure, and peripheral gastroenteropancreatic actions. Circulating ghrelin levels mostly reflect gastric secretion as indicated by evidence that they are reduced by 80% after gastrectomy and even after gastric by-pass surgery. Ghrelin secretion is increased in anorexia and cachexia but reduced in obesity, a notable exception being Prader-Willi syndrome. The negative association between ghrelin secretion and body weight is emphasized by evidence that weight increase and decrease reduces and augments circulating ghrelin levels in anorexia and obesity, respectively, and agrees with the clear negative association between ghrelin and insulin levels. In fact, ghrelin secretion is increased by fasting whereas it is decreased by glucose load as well as during euglycemic clamp but not after arginine or free fatty acid load in normal subjects; in physiological conditions, however, the most remarkable inhibitory input on ghrelin secretion is represented by somatostatin as well as by its natural analog cortistatin that concomitantly reduce β-cell secretion. This evidence indicates that the endocrine pancreas plays a role in directly or indirectly modulating ghrelin secretion. As anticipated, ghrelin, in turn, is expressed within the endocrine pancreas, although it is still matter of debate if it is expressed by β-, α-, or non-α/non-β cells. Moreover, GHS-R1a expression in the pancreas has been demonstrated by many authors. Some impact of synthetic GHS on insulin secretion and glucose metabolism had been reported in both animal and human studies. Depending on dose and experimental conditions ghrelin has been shown able to inhibit or stimulate insulin secretion in animals. In humans, ghrelin administration is followed by transient inhibition of insulin levels that surprisingly follows persistent increase in plasma glucose levels suggesting that ghrelin would also directly or indirectly activate glycogenolisis. Current studies indicate that ghrelin also blunts the insulin response to arginine but not that to oral glucose load in humans. These acute effects of ghrelin are independent of any cholinergic mediation and are not shared by synthetic, peptidyl GHS indicating they are likely mediated by a non-GHS-R1a receptor. These acute effects of ghrelin on insulin secretion would be short-lasting, and it has to be remembered that long-term treatment with synthetic non peptidyl GHS in healthy elderly subjects was followed by insulin resistance. In all, it is already clear that ghrelin has remarkable impact in modulating insulin secretion and glucose metabolism. Insulin and ghrelin secretions seem linked by a negative functional relationship that strengthens the hypothesized role of ghrelin in participating in the management of the neuroendocrine and metabolic response to variations in energy balance.

Effects of Dexamethasone and Alprazolam, a Benzodiazepine, on the Stimulatory Effect of Hexarelin, a Synthetic GHRP, on ACTH, Cortisol and GH Secretion in Humans

Hexarelin (HEX) is a synthetic GHRP which acts on specific receptors at both the pituitary and the hypothalamic level to stimulate GH release both in animals and in humans. Like other GHRPs, HEX possesses also acute ACTH and cortisol-releasing activity similar to that of hCRH. The mechanisms underlying the stimulatory effect of GHRPs on hypothalamo-pituitary-adrenal (HPA) axis are still unclear, although a CNS-mediated action has been demonstrated. In 6 normal healthy young women (26–34 years) we studied the effects on ACTH and cortisol secretion of HEX (2.0 µg/kg i.v. at 0 min) alone and preceded by dexamethasone (DEXA, 1 mg p.o. at 23.00 h on the previous night) or alprazolam (ALP, 0.02 mg/kg p.o. at –90 min), a benzodiazepine which binds to GABA receptors and possesses CRH-mediated inhibitory activity on HPA axis. ACTH and cortisol secretion after saline administration as well as the GH response to HEX alone and preceded by DEXA or ALP were also studied. HEX administration elicited an increase in ACTH (peak vs. baseline, mean ± SEM: 28.0 ± 6.7 vs. 11.7 ± 2.2 pg/ml, p < 0.05) and cortisol secretion (162.6 ± 15.0 vs. 137.7 ± 12.6 µg/l, p < 0.05). DEXA pretreatment strongly inhibited basal ACTH (3.2 ± 0.7 pg/ml, p < 0.01) and cortisol levels (11.3 ± 2.5 µg/l, p < 0.001) and abolished the ACTH and cortisol responses to HEX (3.6 ± 0.9 pg/ml, p < 0.01 and 10.7 ± 2.0 µg/l, p < 0.001), respectively. On the other hand, ALP pretreatment did not significantly modify basal ACTH (7.9 ± 2.0 pg/ml) and cortisol levels (127.6 ± 14.5 µg/l) but abolished the HEX-induced ACTH and cortisol secretions (8.6 ± 2.4 pg/ml, p < 0.05 and 111.0 ± 6.0 µg/l, p < 0.05), respectively. ACTH and cortisol levels after HEX when preceded by ALP overlapped with those recorded during saline. HEX induced a clear GH response (peak at 15 min vs. baseline: 65.5 ± 20.5 vs. 2.2 ± 0.7 µg/l, p < 0.03) which was blunted by ALP (peak at 15 min: 21.5 ± 5.5 µg/l, p < 0.05) while it was not modified by DEXA pretreatment (78.7 ± 7.6 µg/l). In conclusion, our present data demonstrate that the ACTH- and cortisol-releasing effect of HEX is abolished by either dexamethasone or alprazolam, a benzodiazepine, which is even able to blunt the GH-releasing activity of the hexapeptide. These findings suggest that, in physiological conditions, the stimulatory effect of GHRPs on HPA axis is sensitive to the negative glucocorticoid feedback and could be mediated by GABAergic mechanisms; the latter seem also involved in the GH-releasing activity of GHRPs.

Metabolic and cardiovascular profile in patients with Addison’s disease under conventional glucocorticoid replacement

Objective: Although two studies have shown that Addison’s disease (AD) is still a potentially lethal condition for cardiovascular, malignant, and infectious diseases, a recent retrospective study showed a normal overall mortality rate. Differently from secondary hypoadrenalism, scanty data exist on the role of conventional glucocorticoid replacement on metabolic and cardiovascular outcome in AD. Subjects and methods: In 38 AD under conventional glucocorticoid replacement (hydrocortisone 30 mg/day or cortisone 37.5 mg/day) ACTH, plasma renin activity (PRA), DHEAS, fasting glucose and insulin, 2-h glucose after oral glucose tolerance test, serum lipids, 24-h blood pressure and intima-media thickness (IMT) were evaluated and compared with 38 age-, sex- and body mass index (BMI)-matched controls (CS). Results: AD had ACTH and PRA higher and DHEAS lower (p<0.0005) than CS. Mean waist was higher (p<0.05) in AD than in CS. Although no differences were found for mean gluco-lipids levels, a higher percentage of AD compared to CS were IGT (8 vs 0%), hypercholesterolemic (18 vs 8%), and hypertriglyceridemic (18 vs 8%); none of the AD and CS showed either HDL<40 mg/dl or LDL>190 mg/dl. At the multiple regression analysis, in both AD and CS, BMI was the best predictor of 2-h glucose and age of total and LDL cholesterol; in AD, no significant correlation was found between the above mentioned metabolic parameters and either hormone levels or disease duration. In both AD and CS 24-h blood pressure and IMT were normal. Conclusions: Our study shows a higher prevalence of central adiposity, impaired glucose tolerance and dyslipidemia in AD patients.

EP1572: a novel peptido-mimetic GH secretagogue with potent and selective GH-releasing activity in man.

EP1572 (JMV1843 [Aib-DTrp-DgTrp-CHO]) is a new peptido-mimetic GH secretagogue (GHS) showing binding potency to the GHS-receptor in animal and human tissues similar to that of ghrelin and peptidyl GHS. EP1572 induces marked GH increase after sc administration in neonatal rats. Preliminary data in 2 normal young men show that: 1) acute iv EP1572 administration (1.0 μg/kg) induces strong and selective increase of GH levels; 2) single oral EP1572 administration strongly and reproducibly increases GH levels even after a dose as low as 0.06 mg/kg. Thus, EP1572 is a new peptido-mimetic GHS with potent and selective GH-releasing activity.

Elderly subjects show severe impairment of dehydroepiandrosterone sulphate and reduced sensitivity of cortisol and aldosterone response to the stimulatory effect of ACTH1−24

OBJECTIVE Hyperactivity of the hypothalamic‐pituitary‐adrenal (HPA) axis in ageing has been reported both in humans and in animals and may be involved in age‐related changes in body composition, structure functions and metabolism, as well as in brain ageing. Despite the supposed HPA hyperactivity and its refractoriness to negative glucocorticoid feedback, low levels of dehydroepiandrosterone (DHEA) and its sulphate have been clearly demonstrated in human ageing and may suggest another cause of age‐related changes in structure function and metabolism. Thus, our aim was to verify the adrenal responsiveness to various ACTH doses in normal elderly subjects.