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) (PO.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 (PO.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.

Does obestatin modulate the hypothalamic appetite‐regulating network in peripubertal sheep?

“…It is possible that these changes were due to downregulation of the NPY neuronal system. It is interesting that the diminished NPY secretion in prepubertal ewes was observed after the infusion of leptin, another peripheral anorexigenic hormone (Polkowska et al., ; Wójcik‐Gładysz et al., ). It should be emphasized that leptin‐induced changes in the NPY immunoreactivity were restricted to NPY perikarya and varicose nerve fibres located in the ARC nucleus, whereas no effect on subpopulations of NPY neurons in the PEV and paraventricular nucleus (PVN) was found (Polkowska et al., ).…”

Brain-derived neurotrophic factor (BDNF) affects somatotrophic axis activity in sheep

“…The results of our earlier study revealed that in female sheep the main activities of somatostatin-containing neurons in the periventricular nucleus (PEV) are known for their involvement in the control of growth hormone (GH) secretion (Polkowska et al, 2008;Tillet et al, 2010). Additionally, this discrete (specific) population of somatostatin neurons is the most sensitive to the action of the orexigenic and anorexigenic peptides (hormones) like leptin, ghrelin or obestatin (Polkowska et al, 2010;Wójcik-Gładysz et al, 2010.…”