Growth hormone response to GHRH, GHRP-6 and GHRH + GHRP-6 in patients with polycystic ovary syndrome

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

INTRODUCTION

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.

AIM OF THE STUDY

Evaluate the endocrine and metabolic response to ghrelin administration in PCOS obese patients compared to body mass index (BMI)-matched and normal weight women.

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

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

OBJECTIVE

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).

DESIGN

Prospective, controlled study.

SETTING

Academic research environment.

PATIENT(S)

Twenty obese women with PCOS, and 15 obese controls.

INTERVENTION(S)

Oral glucose tolerance test (OGTT) and ghrelin test (1 microg/kg i.v. bolus).

MAIN OUTCOME MEASURE(S)

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.

RESULT(S)

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.

CONCLUSION(S)

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.

Pubertal alterations in growth and body composition: IX. Altered spontaneous secretion and metabolic clearance of growth hormone in overweight youth

Deconvolution analysis was used to determine 12-hour spontaneous nocturnal growth hormone (GH) secretion and GH half-life in lean (body mass index, <85th percentile; n = 39) and overweight (body mass index, > or =85th percentile; n = 18) youth. The integrated GH concentration, GH burst mass, and half-life were lower (P < .05) in overweight than in lean youth. For each unit increase in percentage of body fat, integrated serum GH concentrations, secretory burst mass, and half-life declined by 83.6 microg/L per minute (r = -0.39, P < .01), 0.22 microg/L (r = -0.28, P < .05), and 0.2 minute (r = -0.38, P < .01), respectively. The effect of overweight on GH secretion was independent of pubertal status. Hierarchical regression models tested the hypothesis that altered GH secretion in youth is more related to total adiposity than abdominal visceral fat. When age, sex, fat-free mass, testosterone, and estradiol were held constant, the sequential addition of abdominal visceral fat did not increase R2 for any GH secretion variable. Sequential addition of percentage of body fat increased R2 (P < .05) for integrated GH concentration, total secretory rate, secretory burst mass, and pulsatile production rate. We conclude that serum GH concentrations are reduced in overweight youth primarily because of reduced GH burst mass with no change in the number of secretory events and secondarily to reduced GH half-life. Based on the model that GH-releasing hormone predominantly increases GH pulse amplitude whereas somatostatin primarily controls GH pulse frequency, these results suggest that overweight in youth diminishes GH-releasing hormone stimulation resulting in truncated GH bursts but does not alter the number of somatostatin withdrawal intervals so that GH burst frequency is conserved.

Increased growth hormone response to clonidine in nonobese normoinsulinemic patients with polycystic ovary syndrome

OBJECTIVE

To assess growth hormone (GH) levels in response to acute clonidine stimulation in nonobese patients with polycystic ovary syndrome (PCOS) in comparison to patients with idiopathic hirsutism (IH) and normal women without hirsutism.

DESIGN

Cross-sectional study. Outpatient clinic, Porto Alegre, Brazil.

PATIENT(S)

Fourteen patients with PCOS, 11 women with IH, and 10 age- and weight-matched normal women without hirsutism were studied. All subjects presented normal body mass index (<25 kg/m(2)) and insulin levels (<25 microIU/mL).

INTERVENTION(S)

Growth hormone levels were assessed in all patients before and 30, 60, 90, and 120 minutes after oral administration of 0.3 mg of clonidine.

MAIN OUTCOME MEASURE(S)

Growth hormone levels before and after clonidine administration.

RESULT(S)

Delta GH and GH levels at 30, 60, and 120 minutes were significantly higher in the PCOS group than in the IH and control groups.

CONCLUSION(S)

The greater GH response to clonidine in nonobese normoinsulinemic PCOS patients observed in this study suggests a dysregulation in GH secretion in these patients. Further studies are required to elucidate the role of GH in the pathogenesis of PCOS and to investigate the existence of an association between androgens, IGF-I, and GH modulation in PCOS.

Aspectos neuroendócrinos na síndrome dos ovários policísticos

A síndrome dos ovários policísticos (PCOS) é a endocrinopatia mais freqüente na mulher em idade reprodutiva. O quadro clínico é variável, mas em geral apresenta-se com hirsutismo, acne e/ou alopecia androgênica, anovulação crônica associada a distúrbio menstrual e infertilidade. A resistência insulínica pode estar presente em mais da metade dos casos, em especial nas pacientes obesas. A etiopatogenia ainda não foi totalmente esclarecida, mas mecanismos neuroendócrinos vêm sendo estudados nos últimos anos. Embora esteja bem estabelecida a presença de secreção inapropriada do eixo GnRH-LH em pacientes com PCOS, algumas delas, especialmente as obesas/hiperinsulinêmicas, exibem níveis normais de LH e uma atenuação de sua resposta aos testes de estímulo. Recentemente, descrevemos uma correlação negativa entre leptina e LH em pacientes com PCOS, sugerindo que a atenuação nos níveis de LH nestas pacientes possa estar relacionada a um estado de resistência à leptina. Por outro lado, evidências sugerem que o eixo somatotrófico participe também dos mecanismos fisiopatológicos envolvidos na PCOS. Dados recentes do nosso grupo demonstram que pacientes de peso normal e normoinsulinêmicas apresentam uma maior resposta do GH à clonidina do que pacientes com hirsutismo idiopático. Um mecanismo possível seria uma ação co-gonadotrófica do GH, contribuindo para o hiperandrogenismo clínico e a anovulação. Outra possibilidade é que a elevação da secreção de GH seja somente um epifenômeno vinculado ao aumento de androgênios ovarianos e sua conversão periférica em estrogênios. Estudos futuros são necessários para esclarecer os mecanismos subjacentes associados às alterações descritas neste trabalho e sua relevância na etiopatogenia, diagnóstico e tratamento desta síndrome.

Growth-hormone response to combined stimulation with GHRH plus GH-releasing peptide-6 in obese patients with polycystic ovary syndrome before and after short-term fasting

Controversial data were reported on GH response to different provocative stimuli in obese patients with polycystic ovary syndrome (PCOS). The objective of our study was to assess the effect of short-term fasting on GH response to combined stimulus with GHRH+GH-releasing peptide-6 (GHRP-6) in obese patients with PCOS and possible relation with leptin and insulin changes during fasting. Twelve obese PCOS women and nine obese control women participated in 3-day fasting. GH response, IGF-I, insulin and leptin were measured after GHRH+ GHRP-6, before and after short-term fasting. Obese PCOS patients had significantly greater GH peak after GHRH+GHRP-6 before fasting. Enhanced response to GH stimulation was found after fasting without substantial differences between obese PCOS and obese controls. Insulin and leptin significantly decreased, while insulin sensitivity significantly improved in both groups during fasting. In conclusion, obese PCOS patients have peculiar type of GH response to GHRH+GHRP-6 before fasting, possibly due to enhanced sensitivity of somatotrophs. Observed changes in insulin and leptin may participate in modulation of enhanced GH response after short-term fasting to GHRH+GHRP-6 in PCOS and obese controls.

GH release after GHRH plus arginine administration in obese and overweight women with polycystic ovary syndrome

Few and unclear data are available in the literature about the relationship between impairment of GH/IGF-I axis and polycystic ovary syndrome (PCOS). This study was aimed to evaluate the basal GH and IGF- levels, and GH release after challenge test in obese and overweight women with PCOS. Thirty patients with PCOS and other 30 healthy women matched for age, body mass index (BMI) and waist-hip ratio (WHR) were studied. Serum follicle-stimulating hormone (FSH), LH, PRL, E2, P, 17OH-progesterone (17OH-P), total T, delta4, DHEA-S, SHBG, GH and IGF-I levels were evaluated in each subject. A GHRH plus arginine challenge test was performed in all subjects. After provocative test, in PCOS and control women the GH levels were significantly (p<0.05) higher in comparison to basal values from 30 min to 120 min. At the same times, a significant (p<0.05) difference was observed between women with PCOS in comparison to healthy women. The mean peak value of GH resulted significantly (p<0.05) lower in PCOS women in comparison to healthy women. The total GH response (area under curve, AUC) to GHRH plus arginine test resulted significantly (p<0.05) lower in PCOS than in healthy women. These findings were statistically significant (p<0.05) also considering the distinction in obese and overweight women. The AUC for GH secretion was significantly lower (p<0.05) in obese in comparison to overweight subjects in the control group, whereas no significant difference was detected between obese and overweight women in the PCOS group. In conclusion, in PCOS women there is a BMI-independent alteration of the GH levels. Further investigations will be necessary to establish the real cause of these data.

Growth hormone response to thyrotrophin releasing hormone in women with polycystic ovarian syndrome

Recent clinical studies have suggested that women with polycystic ovarian syndrome (PCOS) may have disturbances of growth hormone (GH) kinetics and the GH/insulin-like growth factor (IGF)-I system. The knowledge that in various metabolic abnormalities there is a paradoxical sensitivity of pituitary somatotrophs to thyrotrophin releasing hormone (TRH) administration led to this investigation of the GH secretory response to TRH in women with PCOS. Twenty-four women with PCOS and 18 control women were studied. TRH was given as a single i.v. injection (time 0) and blood samples for GH measurements were obtained at -15, 0, 15, 30, 60 and 90 min. The GH responses were expressed as the area under the curve (AUC) or the differences from the basal value (Deltamax). The GH response to TRH (mean +/- SEM) was greater in women with PCOS (Deltamax 2.47 +/- 1. 73 versus 0.47 +/- 0.06 ng/ml, P < 0.05 and GH AUC 8.05 +/- 2.10 versus 2.58 +/- 0.18 ng/ml/90 min, P < 0.05). According to GH response to TRH, two PCOS subgroups were identified: (i) normal responders (n = 14) who showed Deltamax GH response (0.36 +/- 0.06 ng/ml)and GH AUC (1.93 +/- 0.64 ng/ml/90 min) similar to that in the controls and (ii) over-responders (n +/- 10) who showed a paradoxical increase in GH concentrations in response to TRH (Deltamax GH response 5.43 +/- 1.27 ng/ml and GH AUC 16.62 +/- 3.51 ng/ml per 90 min) that was significantly higher than in normally responding PCOS patients (P < 0.0001) or in controls (P < 0.0001). These data demonstrate an enhanced GH response to TRH administration in a subgroup of women with PCOS.

Effect of opioid blockade on insulin and growth hormone (GH) secretion in patients with polycystic ovary syndrome: the heterogeneity of impaired GH secretion is related to both obesity and hyperinsulinism

OBJECTIVE

To investigate the involvement of opioid tone, obesity, and hyperinsulinemia in GH secretion in women with polycystic ovary syndrome (PCOS).

DESIGN

Controlled clinical study.

SETTING

Catholic University of Sacred Heart School of Medicine in Rome, Italy.

PATIENT(S)

Twenty-two patients with PCOS and 14 healthy, normally ovulating volunteers, matched for age and body mass index.

INTERVENTION(S)

Patients underwent a GH-releasing hormone (GHRH) test and an oral glucose tolerance test before and after 4-5 weeks of treatment with 50 mg/d of naltrexone.

MAIN OUTCOME MEASURE(S)

Serum concentrations of GH, insulin, glucose, steroids, and gonadotropins, as well as the GH area under the curve (AUC-GH) and the insulin area under the curve (AUC-I), were measured before and after naltrexone treatment.

RESULT(S)

In patients with PCOS, the administration of naltrexone increased the GH response to the GHRH test without interfering with the insulin response to the oral glucose tolerance test. However, the GH response to the GHRH test was improved significantly only in lean patients with PCOS, whereas obese patients with PCOS did not show any improvement in GH secretion. In obese control subjects, the treatment reduced plasma basal insulin concentrations and increased the AUC-GH, whereas in lean control subjects, the treatment reduced the GHRH-induced response. In normoinsulinemic patients with PCOS, the GH response to the GHRH test increased significantly after treatment, whereas the AUC-I was not affected. In hyperinsulinemic patients with PCOS, treatment with naltrexone significantly reduced the AUC-I, whereas the AUC-GH increased only in lean hyperinsulinemic patients with PCOS.

CONCLUSION(S)

Naltrexone treatment improves GHRH-induced GH secretion in patients with PCOS. However, this GH response is heterogeneously represented in relation to both obesity and hyperinsulinism.

Growth hormone (GH) response to GH-releasing peptide-6 in type 1 diabetic patients with exaggerated GH-releasing hormone-stimulated GH secretion

In type 1 diabetes mellitus (DM 1), high GH basal levels and exaggerated GH responses to several stimuli, including GHRH, have been described. GH-releasing peptide-6 (GHRP-6) is a synthetic hexapeptide that specifically stimulates GH release, both in vitro and in vivo. The aim of this study was to evaluate the effects of GHRP-6 alone or in combination with GHRH on GH secretion in DM 1. Six type 1 diabetic males and six age-, sex-, and body mass index-matched control volunteers were studied. Each subject received GHRH (100 microg iv), GHRP-6 (90 microg iv), and GHRH plus GHRP-6 on three separate days. GH peak values were higher in DM 1 patients than in control volunteers, after GHRH (52.2+/-9.8 vs. 19.3+/-6.0 microg/L; P = 0.016), GHRP-6 (66.2+/-9.6 vs. 39.9+/-6.3 microg/L; P = 0.05), and GHRH plus GHRP-6 (81.8+/-4.4 vs. 53.7+/-8.2 microg/L; P = 0.01). An additive GH response to combined administration of these two peptides was observed in diabetic patients. Serum insulin-like growth factor (IGF)-1 levels were diminished in DM 1, with respect to normal subjects (145.2+/-21.5 vs. 269.7+/-42.0 microg/L; P = 0.01), whereas IGF-binding protein-3 levels were not significantly different between DM-1 and controls. In summary, GHRP-6 is a potent stimulus for GH secretion in DM 1. The combined administration of GHRP-6 plus GHRH constitutes the most powerful stimulus for GH secretion in DM 1. These patients exhibit a greater GH secretory capacity than normal subjects, probably caused by a diminished tone in the IGF-1 sustained negative feedback control exerted upon somatotroph responsiveness.

Growth hormone secretagogues in pathological states: diagnostic implications

The identification and cloning of the receptor for synthetic growth hormone (GH) secretagogues, even before the endogenous ligand has been identified or its precise physiological role established, suggests that there is a novel target of action for this class of drug. In an attempt to select patients who will benefit from GH treatment, GH secretagogues are being evaluated for their usefulness in diagnosing GH deficiency. The effects of GH-releasing peptides (GHRPs) on GH release as a function of age and metabolic status, and in different neuroendocrine pathologies, are described, as are the different mechanisms of action, potency and reproducibility of the response to GHRPs compared with GH-releasing hormone (GHRH). GHRPs offer the advantage over GHRH in natural models of deranged GH secretion in that, in various metabolic states (e.g. obesity, anorexia nervosa and non-insulin-dependent diabetes mellitus), the GH response to GHRH is more impaired than it is to GHRPs. However, in some neuroendocrine pathologies, the reverse is true. Thus, both secretagogues provide separate information on the physiological status of somatotrophs.