LH isoform profiles during short-term pulsatile LHRH administration in elderly men

Older men exhibit reduced efficacy of and heightened potency downregulation by intravenous pulses of recombinant human LH: a study in 92 healthy men

Direct sampling of the human spermatic veins has disclosed concomitant LH and testosterone (T) pulses, suggesting pulsatile LH concentration-dependent stimulation of T secretion. However, studies to date have examined this hypothesis using only pharmacological stimulation with hCG. The present study tests the hypothesis that age is marked by decreased T secretory responses to repeated near-physiological iv pulses of recombinant human LH administered in a Clinical Translational Science Center. Participants included 92 healthy men aged 18-75 yr with BMI 18-34 kg/m(2). The contribution of endogenous LH pulses was minimized by combined injection of a selective GnRH receptor antagonist sc and successive pulses of biosynthetic LH iv. A new analytical dose response model was applied to estimate the properties of exogenous LH's drive of T secretion. Regression of LH-T dose response potency estimates on age showed that the efficacy of pulses of biosynthetic LH progressively decreased with age (P = 0.014, r = 0.26). Testis sensitivity to exogenous LH pulses also declined with age (P = 0.011, r = 0.27). Moreover, estimated Leydig cell downregulation by LH pulses rose significantly with age (P = 0.039, r = 0.22). These outcomes were selective, since the recovery potency of infused LH was not affected by age but was reduced by increasing BMI (P = 0.011, r = 0.27). Assuming stable bioactivity of infused recombinant human LH, these novel data indicate that factors associated with age and BMI attenuate LH efficacy and testis sensitivity and augment Leydig cell downregulation in healthy men.

The endocrine response to acute ghrelin administration is blunted in patients with anorexia nervosa, a ghrelin hypersecretory state

OBJECTIVE

Ghrelin, a gastric-derived natural ligand of the GH secretagogue (GHS)-receptor (GHS-R), strongly stimulates GH secretion but also possesses other neuroendocrine actions, stimulates food intake and modulates the endocrine pancreas and energy homeostasis. Ghrelin secretion is negatively modulated by food intake. Similarly, glucose and also insulin probably exert an inhibitory effect on ghrelin secretion. Fasting ghrelin levels are reduced in obesity, elevated in anorexia nervosa and restored by weight recovery. The chronic elevation of circulating ghrelin levels in anorexia suggested the hypothesis of an alteration of the sensitivity to the orexigenic action of ghrelin in this condition. The aim of this study was to define the endocrine actions of ghrelin in patients with anorexia nervosa.

DESIGN

We enrolled nine women with anorexia nervosa of restricter type [AN; age (mean +/- SEM) 24.2 +/- 1.8 years; body mass index (BMI) 14.7 +/- 0.4 kg/m2] and seven normal young women in their early follicular phase as control group (NW; age 30.6 +/- 3.1 years; BMI 20.3 +/- 0.5 kg/m2).

MEASUREMENTS

In all the subjects we studied the GH, PRL, ACTH, cortisol, insulin and glucose responses to acute ghrelin administration (1.0 microg/kg as i.v. bolus). The GH response to GHRH (1.0 microg/kg as i.v. bolus) and basal ghrelin and IGF-I levels were also evaluated in all the subjects.

RESULTS

Basal morning ghrelin and GH levels in AN (643.6 +/- 21.3 ng/l and 10.4 +/- 0.5 microg/l, respectively) were higher (P < 0.05) than in NW (233.5 +/- 14.2 ng/l and 0.7 +/- 0.7 microg/l, respectively). However, IGF-I levels in AN (145.3 +/- 10.9 microg/l) were lower (P < 0.05) than in NW (325.4 +/- 12.6 microg/l). The GH response to GHRH in AN was higher (P < 0.05) than that in NW, but in AN the GH response to ghrelin was lower (P < 0.05) than that in NW. In AN and NW ghrelin also induced similar increases (P < 0.05) in PRL, ACTH and cortisol levels. Ghrelin administration was followed by significant increase in glucose levels in NW (P < 0.05) but not in AN.

CONCLUSIONS

This study demonstrates that anorexia nervosa, a clinical condition of ghrelin hypersecretion, shows a specific reduction in the GH response to ghrelin, despite the hyper-responsiveness to GHRH administration. The impaired GH response to ghrelin in anorexia nervosa agrees with previous evidence of blunted GH response to synthetic GH secretagogues and could reflect desensitization of the GHS receptor induced by the chronic elevation of ghrelin levels in this pathological state.