The effect of intracerebroventricular infusions of ghrelin and/or short fasting on the gene expression and immunoreactivity of somatostatin in the hypothalamic neurons and on pituitary growth hormone in prepubertal female lambs. Morphological arguments

Abstract

The effect of exogenous ghrelin on somatostatin distribution in the ruminant's hypothalamus has not been yet determined. The aim of the present study was to investigate the consequence of central infusion of ghrelin and/or short fasting on the secretory activity of the somatostatin/GH system in prepubertal female sheep. Animals were randomly divided into three groups, two standard fed and one fasted for 72 h. One standard group and one fasted group were infused icv with vehicle, while the remaining standard group was infused with ghrelin (25 μl/120 μl/h). Infusions were performed for 6 h during three consecutive days; blood samples were collected during the “day 0” (before the infusion) and “day 3” Immediately after the experiment the sheep were slaughtered. Parts of the brains were fixed in situ for further immunohistochemical analysis The remaining brains were frozen for RT-PCR analysis. Fasting and ghrelin infusion elicited the same kind of changes in the secretory activity of the somatostatin/GH system compared to standard fed sheep. The expression of somatostatin mRNA and ir somatostatin in the PEV nucleus and ir stores in the median eminence increased in both these groups compared to standard fed sheep (P < 0.001). The population of ir GH pituitary cells decreased (P < 0.001), the mean GH plasma concentrations increased in all fasted and ghrelin infused animals between day 0 and day 3 of infusions (P < 0.05) compared to the standard fed group. It can be suggested that ghrelin takes part in the mechanisms linking the nutritional status of an organism with an activity of the somatotrophic axis on the level of the CNS by stimulating GH release through suppression of the somatostatin output.