Acute intravenous acyl ghrelin infusion induces thirst but does not affect sodium excretion: two randomized, double-blind, placebo-controlled crossover studies in hypopituitary patients

OBJECTIVE

Acyl ghrelin, which is the endogenous ligand for the growth hormone secretagogue receptor, potently stimulates pituitary growth hormone release, and to some degree adrenocorticotropic hormone and prolactin. Ghrelin is also orexigenic and has recently been shown to stimulate renal sodium absorption in rodent models. Increased thirst sensation has been observed as a side effect of acyl ghrelin administration in some human studies. The objective of this clinical trial was to investigate the direct effects of acyl ghrelin on thirst sensation and sodium excretion in hypopituitary patients.

DESIGN

Hypopituitary patients on stable replacement with hydrocortisone and growth hormone were investigated in two double-blind and placebo-controlled crossover studies. The patients received a 5-h intravenous infusion of acyl ghrelin (5 pmol/kg/min in the first study and 1 pmol/kg/min in the second study). Thirst sensation was measured on a Visual Analog Scale (VAS). In the second study plasma osmolality, vasopressin, copeptin, water intake, diuresis and urinary excretion of sodium and creatinine were measured.

RESULTS

In the initial study, acyl ghrelin (5 pmol/kg/min) increased thirst sensation (time × treatment analysis of variance for the effect of acyl ghrelin infusion P = 0.003). In the second study acyl ghrelin (1 pmol/kg/min) also increased thirst (P = 0.04) but did not affect urinary excretion of either sodium or water.

CONCLUSIONS

We demonstrate that acyl ghrelin infusion increases thirst sensation, without affecting sodium excretion or diuresis in human subjects.

Ghrelin for the management of cachexia associated with cancer

BACKGROUND

Cancer sufferers are amongst the most malnourished of all the patient groups. Studies have shown that ghrelin, a gut hormone can be a potential therapeutic agent for cachexia (wasting syndrome) associated with cancer. A variety of mechanisms of action of ghrelin in people with cancer cachexia have been proposed. However, safety and efficacy of ghrelin for cancer-associated cachexia have not been systematically reviewed. The aim of this review was to assess whether ghrelin is associated with better food intake, body composition and survival than other options for adults with cancer cachexia.

OBJECTIVES

To assess the efficacy and safety of ghrelin in improving food intake, body composition and survival in people with cachexia associated with cancer.

SEARCH METHODS

We searched CENTRAL, MEDLINE and Embase without language restrictions up to July 2017. We also searched for ongoing studies in trials registers, performed handsearching, checked bibliographic references of relevant articles and contacted authors and experts in the field to seek potentially relevant research. We applied no restrictions on language, date, or publication status.

SELECTION CRITERIA

We included randomised controlled (parallel-group or cross-over) trials comparing ghrelin (any formulation or route of administration) with placebo or an active comparator in adults (aged 18 years and over) who met any of the international criteria for cancer cachexia.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for eligibility. Two review authors then extracted data and assessed the risk of bias for individual studies using standard Cochrane methodology. For dichotomous variables, we planned to calculate risk ratio with 95% confidence intervals (CI) and for continuous data, we planned to calculate mean differences (MD) with 95% CI. We assessed the evidence using GRADE and created 'Summary of findings' tables.

MAIN RESULTS

We screened 926 individual references and identified three studies that satisfied the inclusion criteria. Fifty-nine participants (37 men and 22 women) aged between 54 and 78 years were randomised initially, 47 participants completed the treatment. One study had a parallel design and two had a cross-over design. The studies included people with a variety of cancers and also differed in the dosage, route of administration, frequency and duration of treatment.One trial, which compared ghrelin with placebo, found that ghrelin improved food intake (very low-quality evidence) and had no adverse events (very low-quality evidence). Due to unavailability of data we were unable to report on comparisons for ghrelin versus no treatment or alternative experimental treatment modalities, or ghrelin in combination with other treatments or ghrelin analogues/ghrelin mimetics/ghrelin potentiators. Two studies compared a higher dose of ghrelin with a lower dose of ghrelin, however due to differences in study designs and great diversity in the treatment provided we did not pool the results. In both trials, food intake did not differ between participants on higher-dose and lower-dose ghrelin. None of the included studies assessed data on body weight. One study reported higher adverse events with a higher dose as compared to a lower dose of ghrelin.All studies were at high risk of attrition bias and bias for size of the study. Risk of bias in other domains was unclear or low.We rated the overall quality of the evidence for primary outcomes (food intake, body weight, adverse events) as very low. We downgraded the quality of the evidence due to lack of data, high or unclear risk of bias of the studies and small study size.

AUTHORS' CONCLUSIONS

There is insufficient evidence to be able to support or refute the use of ghrelin in people with cancer cachexia. Adequately powered randomised controlled trials focusing on evaluation of safety and efficacy of ghrelin in people with cancer cachexia is warranted.

Metabolic responses to exogenous ghrelin in obesity and early after Roux-en-Y gastric bypass in humans

AIMS

Ghrelin is a gastric-derived hormone that stimulates growth hormone (GH) secretion and has a multi-faceted role in the regulation of energy homeostasis, including glucose metabolism. Circulating ghrelin concentrations are modulated in response to nutritional status, but responses to ghrelin in altered metabolic states are poorly understood. We investigated the metabolic effects of ghrelin in obesity and early after Roux-en-Y gastric bypass (RYGB).

MATERIALS AND METHODS

We assessed central and peripheral metabolic responses to acyl ghrelin infusion (1 pmol kg^-1  min^-1 ) in healthy, lean subjects (n = 9) and non-diabetic, obese subjects (n = 9) before and 2 weeks after RYGB. Central responses were assessed by GH and pancreatic polypeptide (surrogate for vagal activity) secretion. Peripheral responses were assessed by hepatic and skeletal muscle insulin sensitivity during a hyperinsulinaemic-euglycaemic clamp.

RESULTS

Ghrelin-stimulated GH secretion was attenuated in obese subjects, but was restored by RYGB to a response similar to that of lean subjects. The heightened pancreatic polypeptide response to ghrelin infusion in the obese was attenuated after RYGB. Hepatic glucose production and hepatic insulin sensitivity were not altered by ghrelin infusion in RYGB subjects. Skeletal muscle insulin sensitivity was impaired to a similar degree in lean, obese and post-RYGB individuals in response to ghrelin infusion.

CONCLUSIONS

These data suggest that obesity is characterized by abnormal central, but not peripheral, responsiveness to ghrelin that can be restored early after RYGB before significant weight loss. Further work is necessary to fully elucidate the role of ghrelin in the metabolic changes that occur in obesity and following RYGB.

Short-term estradiol supplementation potentiates low-dose ghrelin action in the presence of GHRH or somatostatin in older women

CONTEXT

Ghrelin is a potent gastric-derived GH-releasing peptide. How ghrelin interacts with sex steroids, GHRH, and somatostatin (SS) is not known.

OBJECTIVE

Our objective was to test the hypotheses that ghrelin's interactions with GHRH (synergistic) and SS (disinhibitory) are ghrelin dose-dependent and amplified by estrogen. SUBJECTS, SETTING, AND DESIGN: Healthy postmenopausal women were treated with placebo (n=12) or 17β-estradiol (E2) (n=12) at the Center for Translational Science Activities in a randomized double-blind prospective study.

METHODS

Ghrelin dose-dependence was assessed by nonlinear curve fitting of the relationship between deconvolved GH secretory-burst mass and 5 randomly ordered ghrelin doses (0, 0.03, 0.135, 0.6, and 2.7 μg/kg bolus iv) during saline, GHRH, and SS infusion.

RESULTS

Under placebo, neither GHRH nor SS altered the ED50 of ghrelin (range 0.64-0.67 μg/kg). Under E2 (median E2 88 pg/mL), the ED50 of ghrelin declined in the presence of GHRH to 0.52 μg/kg. In contrast, the efficacy of ghrelin rose markedly during GHRH vs saline exposure with and without E2: placebo and saline 52±1.0 vs GHRH 173±3.8 μg/L; and E2 and saline 56±0.90 vs GHRH 174±3.7 μg/L. Sensitivity to ghrelin was similar under all conditions.

SUMMARY

Short-term E2 supplementation in postmenopausal women reduces the ED50 (increases the potency) of ghrelin when GHRH is present, without altering ghrelin efficacy (maximal effect) or hypothalamo-pituitary sensitivity (slope of dose response) to ghrelin. The data suggest possible physiological interactions among sex steroids (endogenous), ghrelin, and GHRH during E2 replacement in postmenopausal women.

Clinical effects of ghrelin on gastrointestinal involvement in patients with systemic sclerosis

The majority of patients with systemic sclerosis (SSc) have gastrointestinal (GI) tract involvement, but therapies using prokinetic agents are usually unsatisfactory. Ghrelin stimulates gastric motility in healthy human volunteers. In this study, we investigated whether ghrelin could improve gastric emptying in patients with gastrointestinal symptoms due to SSc. The study was performed in a randomized, double-blind, placebo-controlled crossover fashion on two occasions. Ten SSc patients with GI tract involvement received an infusion of either ghrelin (5.0 μg/kg) or saline, and gastric emptying rate was evaluated by ¹³C-acetic acid breath test. Gastric emptying was significantly accelerated by ghrelin infusion in patients with SSc (ghrelin vs. saline: 43.3 ± 11.4 min vs. 53.4 ± 5.4 min, P=0.03). No serious adverse effects were observed. Our results suggest that ghrelin might represent a new therapeutic approach for GI tract involvement in patients with SSc.

Growth hormone axis and aging

Growth hormone (GH) and/or ghrelin mimetics represent potential treatment and/or prevention options for musculoskeletal impairment associated with aging. Use of improvement in muscle function as an outcome in studies of GH and ghrelin mimetics is complicated by the lack of a standardized definition for clinically meaningful efficacy of this end point. Based on preliminary study results, the use of ghrelin mimetics may be more suitable for use in this age group than GH itself. There are still several unanswered questions related to the use of ghrelin mimetics in the elderly, which prevents recommendation for its use at the current time.

Physiologic concentrations of exogenously infused ghrelin reduces insulin secretion without affecting insulin sensitivity in healthy humans

BACKGROUND

Infusion of ghrelin to supraphysiologic levels inhibits glucose-stimulated insulin secretion, reduces insulin sensitivity, and worsens glucose tolerance in humans.

OBJECTIVE

The purpose of this study was to determine the effects of lower doses of ghrelin on insulin secretion and insulin sensitivity in healthy men and women.

METHODS

Acyl ghrelin (0.2 and 0.6 nmol kg(-1) h(-1)) or saline was infused for 225 minutes in 16 healthy subjects on 3 separate occasions in randomized order. An i.v. glucose tolerance test was performed, and the insulin sensitivity index (SI) was derived from the minimal model. Insulin secretion was measured as the acute insulin response to glucose (AIRg) and the disposition index was computed as AIRg × SI.

RESULTS

Ghrelin infusions at 0.2 and 0.6 nmol kg(-1) h(-1) raised steady-state plasma total ghrelin levels 2.2- and 6.1-fold above fasting concentrations. Neither dose of ghrelin altered fasting plasma insulin, glucose, or SI, but both doses reduced insulin secretion compared with the saline control, computed either as AIRg (384 ± 75 and 354 ± 65 vs 520 ± 110 pM · min [mean ± SEM], respectively; P < .01 for both low- and high-dose vs saline) or disposition index (2238 ± 421 and 2067 ± 396 vs 3339 ± 705, respectively; P < .02 for both comparisons). The high-dose ghrelin infusion also decreased glucose tolerance.

CONCLUSIONS

Ghrelin infused to levels occurring in physiologic states such as starvation decreases insulin secretion without affecting insulin sensitivity. These findings are consistent with a role for endogenous ghrelin in the regulation of insulin secretion and suggest that ghrelin antagonism could improve β-cell function.

Clinical review: The human experience with ghrelin administration

CONTEXT

Ghrelin is an endogenous stimulator of GH and is implicated in a number of physiological processes. Clinical trials have been performed in a variety of patient populations, but there is no comprehensive review of the beneficial and adverse consequences of ghrelin administration to humans.

EVIDENCE ACQUISITION

PubMed was utilized, and the reference list of each article was screened. We included 121 published articles in which ghrelin was administered to humans.

EVIDENCE SYNTHESIS

Ghrelin has been administered as an infusion or a bolus in a variety of doses to 1850 study participants, including healthy participants and patients with obesity, prior gastrectomy, cancer, pituitary disease, diabetes mellitus, eating disorders, and other conditions. There is strong evidence that ghrelin stimulates appetite and increases circulating GH, ACTH, cortisol, prolactin, and glucose across varied patient populations. There is a paucity of evidence regarding the effects of ghrelin on LH, FSH, TSH, insulin, lipolysis, body composition, cardiac function, pulmonary function, the vasculature, and sleep. Adverse effects occurred in 20% of participants, with a predominance of flushing and gastric rumbles and a mild degree of severity. The few serious adverse events occurred in patients with advanced illness and were not clearly attributable to ghrelin. Route of administration may affect the pattern of adverse effects.

CONCLUSIONS

Existing literature supports the short-term safety of ghrelin administration and its efficacy as an appetite stimulant in diverse patient populations. There is some evidence to suggest that ghrelin has wider ranging therapeutic effects, although these areas require further investigation.

Ghrelin counteracts salt-induced hypertension via promoting diuresis and renal nitric oxide production in Dahl rats

Ghrelin is the endogenous ligand for the growth hormone-secretagogue receptor expressed in various tissues including the heart, blood vessels and kidney. This study sought to determine the effects of long-term treatment with ghrelin (10 nmol/kg, twice a day, intraperitoneally) on the hypertension induced by high salt (8.0% NaCl) diet in Dahl salt-sensitive hypertensive (DS) rats. Systolic blood pressure (SBP) was measured by a tail cuff method. During the treatment period for 3 weeks, high salt diet increased blood pressure compared to normal salt (0.3% NaCl) diet, and this hypertension was partly but significantly (P<0.01) attenuated by simultaneous treatment with ghrelin. Ghrelin significantly increased urine volume and tended to increase urine Na⁺ excretion. Furthermore, ghrelin increased urine nitric oxide (NO) excretion and tended to increase renal neuronal nitric oxide synthase (nNOS) mRNA expression. Ghrelin did not alter the plasma angiotensin II level and renin activity, nor urine catecholamine levels. Furthermore, ghrelin prevented the high salt-induced increases in heart thickness and plasma ANP mRNA expression. These results demonstrate that long-term ghrelin treatment counteracts salt-induced hypertension in DS rats primarily through diuretic action associated with increased renal NO production, thereby exerting cardio-protective effects.

Effects of ghrelin, growth hormone-releasing peptide-6, and growth hormone-releasing hormone on growth hormone, adrenocorticotropic hormone, and cortisol release in type 1 diabetes mellitus

In type 1 diabetes mellitus (T1DM), growth hormone (GH) responses to provocative stimuli are normal or exaggerated, whereas the hypothalamic-pituitary-adrenal axis has been less studied. Ghrelin is a GH secretagogue that also increases adrenocorticotropic hormone (ACTH) and cortisol levels, similarly to GH-releasing peptide-6 (GHRP-6). Ghrelin's effects in patients with T1DM have not been evaluated. We therefore studied GH, ACTH, and cortisol responses to ghrelin and GHRP-6 in 9 patients with T1DM and 9 control subjects. The GH-releasing hormone (GHRH)-induced GH release was also evaluated. Mean fasting GH levels (micrograms per liter) were higher in T1DM (3.5 ± 1.2) than in controls (0.6 ± 0.3). In both groups, ghrelin-induced GH release was higher than that after GHRP-6 and GHRH. When analyzing Δ area under the curve (ΔAUC) GH values after ghrelin, GHRP-6, and GHRH, no significant differences were observed in T1DM compared with controls. There was a trend (P = .055) to higher mean basal cortisol values (micrograms per deciliter) in T1DM (11.7 ± 1.5) compared with controls (8.2 ± 0.8). No significant differences were seen in ΔAUC cortisol values in both groups after ghrelin and GHRP-6. Mean fasting ACTH values were similar in T1DM and controls. No differences were seen in ΔAUC ACTH levels in both groups after ghrelin and GHRP-6. In summary, patients with T1DM have normal GH responsiveness to ghrelin, GHRP-6, and GHRH. The ACTH and cortisol release after ghrelin and GHRP-6 is also similar to controls. Our results suggest that chronic hyperglycemia of T1DM does not interfere with GH-, ACTH-, and cortisol-releasing mechanisms stimulated by these peptides.

Adrenocorticotrophic hormone (ACTH) responsiveness to ghrelin increases after 6 months of ketoconazole use in patients with Cushing's disease: comparison with GH-releasing peptide-6 (GHRP-6)

BACKGROUND

In Cushing's disease (CD), adrenocorticotrophic hormone (ACTH)/cortisol responses to growth hormone secretagogues (GHS), such as ghrelin and GHRP-6, are exaggerated. The effect of clinical treatment of hypercortisolism with ketoconazole on ACTH secretion in CD is controversial. There are no studies evaluating ACTH/cortisol responses to GHS after prolonged ketoconazole use in these patients.

OBJECTIVE

To compare ghrelin- and GHRP-6-induced ACTH/cortisol release before and after ketoconazole treatment in patients with CD.

DESIGN/PATIENTS

Eight untreated patients with CD (BMI: 28.5 +/- 0.8 kg/m(2)) were evaluated before and after 3 and 6 months of ketoconazole treatment and compared with 11 controls (BMI: 25.0 +/- 0.8).

RESULTS

After ketoconazole use, mean urinary free cortisol values decreased significantly (before: 613.6 +/- 95.2 nmol/24 h; 3rd month: 170.0 +/- 27.9; 6th month: 107.9 +/- 30.1). The same was observed with basal serum cortisol (before: 612.5 +/- 69.0 nmol/l; 3rd month: 463.5 +/- 44.1; 6th month: 402.8 +/- 44.1) and ghrelin- and GHRP-6-stimulated peak cortisol levels (before: 1183.6 +/- 137.9 and 1045.7 +/- 132.4; 3rd month: 637.3 +/- 69.0 and 767.0 +/- 91.0; 6th month: 689.8 +/- 74.5 and 571.1 +/- 71.7 respectively). An increase in basal ACTH (before: 11.2 +/- 1.6 pmol/l; 6th month: 19.4 +/- 2.7) and in ghrelin-stimulated peak ACTH values occurred after 6 months (before: 59.8 +/- 15.4; 6th month: 112.0 +/- 11.2). GHRP-6-induced ACTH release also increased (before: 60.7 +/- 17.2; 6th month: 78.5 +/- 12.1), although not significantly.

CONCLUSIONS

The rise in basal ACTH levels during ketoconazole treatment in CD could be because of the activation of normal corticotrophs, which were earlier suppressed by hypercortisolism. The enhanced ACTH responses to ghrelin after ketoconazole in CD could also be due to activation of the hypothalamic-pituitary-adrenal axis and/or to an increase in GHS-receptors expression in the corticotroph adenoma, consequent to reductions in circulating glucocorticoids.

Effects of acute administration of acylated and unacylated ghrelin on glucose and insulin concentrations in morbidly obese subjects without overt diabetes

OBJECTIVE

To investigate the effects of unacylated ghrelin (UAG) and co-administration of acylated ghrelin (AG) and UAG in morbid obesity, a condition characterized by insulin resistance and low GH levels.

DESIGN AND METHOD

Eight morbidly obese non-diabetic subjects were treated with either UAG 200 microg, UAG 100 microg in combination with AG 100 microg (Comb) or placebo in three episodes of 4 consecutive days in a double-blind randomized crossover design. Study medication was administered as daily single i.v. bolus injections at 0900 h after an overnight fast. At 1000 h, a standardized meal was served. Glucose, insulin, GH, free fatty acids (FFA) and ghrelin were measured up to 4 h after administration.

RESULTS

Insulin concentrations significantly decreased after acute administration of Comb only, reaching a minimum at 20 min: 58.2 + or - 3.9% of baseline versus 88.7 + or - 7.2 and 92.7 + or - 2.6% after administration of placebo and UAG respectively (P<0.01). After 1 h, insulin concentration had returned to baseline. Glucose concentrations did not change after Comb. However, UAG administration alone did not change glucose, insulin, FFA or GH levels.

CONCLUSION

Co-administration of AG and UAG as a single i.v. bolus injection causes a significant decrease in insulin concentration in non-diabetic subjects suffering from morbid obesity. Since glucose concentration did not change in the first hour after Comb administration, our data suggest a strong improvement in insulin sensitivity. These findings warrant studies in which UAG with or without AG is administered for a longer period of time. Administration of a single bolus injection of UAG did not influence glucose and insulin metabolism.

On the central mechanism underlying ghrelin's chronic pro-obesity effects in rats: new insights from studies exploiting a potent ghrelin receptor antagonist

In the present study, we explore the central nervous system mechanism underlying the chronic central effects of ghrelin with respect to increasing body weight and body fat. Specifically, using a recently developed ghrelin receptor antagonist, GHS-R1A (JMV2959), we investigate the role of GHS-R1A in mediating the effects of ghrelin on energy balance and on hypothalamic gene expression. As expected, in adult male rats, chronic central treatment with ghrelin for 14 days, when compared to vehicle-treated control rats, resulted in an increased body weight, lean mass and fat mass (assessed by dual X-ray absorptiometry), dissected white fat pad weight, cumulative food intake, food efficiency, respiratory exchange ratio and a decrease of energy expenditure. Co-administration of the ghrelin receptor antagonist JMV2959 suppressed/blocked the majority of these effects, with the notable exception of ghrelin-induced food intake and food efficiency. The hypothesis emerging from these data, namely that GHS-R1A mediates the chronic effects of ghrelin on fat accumulation, at least partly independent of food intake, is discussed in light of the accompanying data regarding the hypothalamic genes coding for peptides and receptors involved in energy balance regulation, which were found to have altered expression in these studies.

Ghrelin increases hunger and food intake in patients with restricting-type anorexia nervosa: a pilot study

Ghrelin increases hunger sensation and food intake in various patients with appetite loss. Anorexia nervosa (AN) begins with psychological stress-induced anorexia and some patients cannot increase their food intake partly because of malnutrition-induced gastrointestinal dysfunction. The effects of ghrelin on appetite, food intake and nutritional parameters in anorexia nervosa (AN) patients were examined. Five female restricting- type AN patients (age: 14-35 y; body mass index: 10.2-14.6 kg/m(2)) had persistently complained of gastrointestinal symptoms and failed to increase body weight. They were hospitalized for 26 days (6 days' pretreatment, 14 days' ghrelin-treatment, and 6 days' post-treatment) and received an intravenous infusion of 3 microg/kg ghrelin twice a day. Ghrelin infusion improved epigastric discomfort or constipation in 4 patients, whose hunger scores evaluated by visual analogue scale questionnaires also increased significantly after ghrelin infusion. Daily energy intake during ghrelin infusion increased by 12-36 % compared with the pre-treatment period. Serum levels of total protein and triglyceride as nutritional parameters significantly increased after ghrelin treatment. There were no serious adverse effects including psychological symptoms. We found that ghrelin decreases gastrointestinal symptoms and increases hunger sensation and daily energy intake without serious adverse events in AN patients. Although the present study had major limitations of the lack of a randomized, placebo-controlled group, non-blindness of the investigators and the small number of patients recruited, it would contribute to further investigations for therapeutic potential of ghrelin in AN patients.

Estrogen supplementation selectively enhances hypothalamo-pituitary sensitivity to ghrelin in postmenopausal women

CONTEXT

Sex-steroid hormones amplify pulsatile GH secretion by unknown mechanisms. Ghrelin is the most potent natural GH secretagogue discovered to date. A plausible unifying postulate is that estradiol (E(2)) enhances hypothalamo-pituitary sensitivity to ghrelin (a physiological effect). The hypothesis is relevant to understanding the basis of hyposomatotropism in aging and other relatively hypogonadal states.

OBJECTIVE

Our objective was to test the hypothesis that E(2) supplementation potentiates ghrelin's stimulation of pulsatile GH secretion.

SETTING

The study was conducted at an academic medical center.

SUBJECTS

Healthy postmenopausal women (n = 20) were included in the study.

INTERVENTIONS

Separate-day iv infusions of saline vs. five graded doses of ghrelin were performed in volunteers prospectively randomly assigned to receive (n = 8) or not receive (n = 12) transdermal E(2) for 21 d were performed.

MEASURES

GH secretion was estimated by deconvolution analysis and abdominal visceral fat mass determined by computerized axial tomography were calculated.

RESULTS

E(2) supplementation augmented ghrelin's stimulation of basal (nonpulsatile) GH secretion by 3.6-fold (P = 0.022), increased GH responses to low-dose ghrelin by 2.9-fold (P = 0.035), did not alter ghrelin efficacy, and elicited more regular patterns of acylated ghrelin concentrations during saline infusion (P = 0.033). Abdominal visceral fat negatively determined responses to ghrelin (R = -0.346; P < 0.005).

CONCLUSIONS

Transdermal E(2) supplementation potentiates GH secretion stimulated by physiological but not pharmacological concentrations of acylated ghrelin, and concomitantly regularizes patterns of bioactive ghrelin secretion in postmenopausal women. Accordingly, the estrogen milieu appears to control sensitivity of the hypothalamopituitary unit to acylated ghrelin.

Repeated administration of ghrelin to patients with functional dyspepsia: its effects on food intake and appetite

BACKGROUND

Ghrelin plays a major role in the regulation of food intake (FI), which makes it a strong candidate for the treatment of anorexia.

OBJECTIVE

We attempted to evaluate the clinical response to repeated ghrelin administration in patients with anorexia caused by functional disorders, such as functional dyspepsia (FD).

SUBJECTS AND METHODS

Subjects included in this study were those who 1) were diagnosed with functional anorexia, including FD and other eating disorders with the exception of anorexia nervosa; 2) were lean (body mass index (BMI)<22 kg/m(2)); and 3) exhibited decreased FI. Subjects received an i.v. infusion of ghrelin (3 microg/kg) for 30 min twice a day (before breakfast and dinner) for 2 weeks. We investigated the effects of ghrelin administration on FI, appetite, hormones, and metabolic parameters.

RESULTS

Six patients with FD were enrolled in this study. Ghrelin administration tended to increase daily FI in comparison with levels before and after completion of treatment, but this difference that was the primary endpoint of this study did not reach statistical significance (P=0.084). Hunger sensation was significantly elevated at the end of drip infusion (P<0.0001). No severe adverse effects were observed.

CONCLUSIONS

These results suggest that ghrelin administration is safe and that this treatment has stimulatory effects on appetite in patients with FD. Further studies are necessary to confirm the efficacy of ghrelin treatment for anorexia-related disorders.

Decreased ghrelin-induced GH release in thyrotoxicosis: comparison with GH-releasing peptide-6 (GHRP-6) and GHRH

In thyrotoxicosis GH response to several stimuli is impaired, but there is no data on ghrelin-induced GH release in these patients. Ghrelin is a potent GH secretagogue and it also increases glucose levels in men. The aim of this study was to evaluate the effects of ghrelin (1 microg/kg), GHRP-6 (1 mug/kg) and GHRH (100 microg), i.v., on GH levels in 10 hyperthyroid patients and in 8 controls. Glucose levels were also measured during ghrelin and GHRP-6 administration. In control subjects and hyperthyroid patients peak GH (microg/l; mean +/- SE) values after ghrelin injection (controls: 66.7 +/- 13.6; hyper: 19.3 +/- 2.4) were significantly higher than those obtained after GHRP-6 (controls: 26.7 +/- 5.1; hyper: 12.6 +/- 1.3) and GHRH (controls: 13.5 +/- 4.3; hyper: 5.3 +/- 1.3). There was a significant decrease in GH responsiveness to ghrelin, GHRP-6 and GHRH in the hyperthyroid group compared to controls. In control subjects and hyperthyroid patients basal glucose (mmol/l) values were 4.5 +/- 0.1 and 4.7 +/- 0.2, respectively. There was a significant increase in glucose levels 30 min after ghrelin injection (controls: 4.9 +/- 0.1; hyper: 5.2 +/- 0.2), which remained elevated up to 120 min. When the two groups were compared no differences in glucose values were observed. GHRP-6 administration was not able to increase glucose levels in both groups. Our data shows that GH release after ghrelin, GHRP-6 and GHRH administration is decreased in thyrotoxicosis. This suggests that thyroid hormone excess interferes with GH-releasing pathways activated by these peptides. Our results also suggest that ghrelin's ability to increase glucose levels is not altered in thyrotoxicosis.

Decreased GH secretion and enhanced ACTH and cortisol release after ghrelin administration in Cushing's disease: comparison with GH-releasing peptide-6 (GHRP-6) and GHRH

GH responsiveness to GH secretagogues (GHS) is blunted in Cushing's disease (CD), while ACTH/cortisol responses are enhanced, by mechanisms still unclear. Ghrelin, the endogenous ligand for GHS-receptors (GHS-R), increases GH, ACTH, cortisol and glucose levels in humans. This study evaluated the GH, ACTH, cortisol and glucose-releasing effects of ghrelin in CD in comparison with GHRP-6. GHRH-induced GH release was also studied. Ten patients with CD (BMI 26.9+/-1.0 kg/m(2)) and ten controls (BMI 24.4+/-1.1 kg/m(2)) received ghrelin (1 microg/kg), GHRP-6 (1 microg/kg) and GHRH (100 microg) separately. GH, ACTH, cortisol and glucose levels were measured. In CD ghrelin-induced GH (microg/L; mean +/- SE) release (peak: 7.2+/-3.0) was higher than seen with GHRP-6 (2.7+/-1.0) and GHRH (0.7+/-0.2), but lower than in controls (ghrelin: 58.3+/-12.1; GHRP-6: 22.9+/-4.8; GHRH: 11.3+/-3.7). In controls ACTH (pg/mL) release after ghrelin (79.2+/-26.8) was higher than after GHRP-6 (23.6+/-5.7). In CD these responses (ghrelin: 192+/-43; GHRP-6: 185+/-56) were similar, and enhanced compared to controls. The same was observed with cortisol. Glucose levels failed to increase after ghrelin in CD, differently than in controls. Our data suggests that hypothalamic and pituitary pathways of GH release activated by ghrelin, GHRP-6 and GHRH are deranged in chronic hypercortisolism. The increased ACTH/cortisol responses to ghrelin and GHRP-6 in CD could be mediated by overexpression of GHS-R in ACTH-secreting adenomas. Hypercortisolism apparently impairs the ability of ghrelin to increase glucose levels.