The effect of intracerebroventricular infusion of leptin on the secretory activity of the somtotropic axis in fasted prepubertal lambs

A Wójcik-Gładysz,T Misztal,K Romanowicz,D Szczepankiewicz,J Polkowska,M Wańkowska

doi:10.22358/jafs/66301/2010

Abstract

The aim of the present study was to investigate the effect of exogenous leptin on somatotrophic axis regulation in prepubertal female lambs under conditions of acute undernutrition (72 h fasting). The analyses in fasted sheep revealed enhancement of immunoreactive (ir) somatostatin stores in perikarya of the periventricular (PEV) nucleus and in terminals of the median eminence (ME) (P<0.001), enhancement of growth hormone (GH) mRNA expression in the adenohypophysis, diminishing of ir GH stores in somatotrophs in the adenohypophysis (P<0.001), and a rise in GH pulsatility (P<0.05) in the blood in comparison with standard-fed sheep. In fasted sheep infused with leptin, additional enhancement of ir somatostatin stores in the PEV nucleus and in the ME (P<0.001), an increase in GH mRNA expression in the adenohypophysis (P<0.001), and augmentation of GH pulsatility (P<0.05) in the blood plasma were noted. In conclusion, acute undernutrition affects somatotrophic axis by enhancement of GH secretion via restraining of somatostatin output. Exogenous leptin additionally amplifies this effect by suppressing somatostatin release and increasing of GH secretion. The results provide evidence that leptin can regulate somatotrophic axis activity in prepubertal female lambs under conditions of acute fasting.

Highlights

Somatic growth processes in mammals are sensitive to the availability of energy from a feed
Immunoreactive somatostatin perikarya created a distinct centre located in the PEV nucleus extending from the suprachiasmatic area in the anterior hypothalamus up to the paraventricular zone in the medial basal hypothalamus
The presented results show that under conditions of acute fasting infusions of leptin into the III ventricle of the brain of prepubertal female lambs suppresses the secretory activity of somatostatin neurons in the hypothalamus, enhances expression of growth hormone (GH) mRNA, and increases GH secretion in adenohypophyseal cells and the release of GH from GH-producing cells into the blood circulation

Summary

Introduction

Somatic growth processes in mammals are sensitive to the availability of energy from a feed. Acute modifications in the nutritional status of animal's organism affect hypothalamo-pituitary-somatotrophic (HPS) axis activity (Casanueva and Dieguez, 1999), and fasting or some food restriction resulted in variations of pulsatile growth hormone (GH) secretion, the principal hormone of HPS axis coordinating postnatal growth in mammals (Polkowska et al, 1996). These modifications are due to secretion of growth hormone releasing hormone and somatostatin, the two main hypothalamic hormones involved in GH regulation (Brazeau et al, 1973, 1984). A stimulatory effect of restricted feeding on GH secretion resulted from attenuation of somatostatin output (Gladysz et al, 2001)

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