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

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.