Obestatin stimulates the somatotrophic axis activity in sheep.

The effects of obestatin (an anorexigenic peripheral peptide) on somatotrophic axis activity in ruminants have not yet been determined. The aim of this study was to investigate the consequence of intracerebroventricular infusions of obestatin on the activity of the somatotrophic axis in peripubertal female sheep. Animals were randomly divided into two groups: control group received intracerebroventricular infusions of the vehicle, and the obestatin group was infused with obestatin (25 µg/120 µL h −1 ). The series of four hourly infusions on three consecutive days were performed. The blood samples were collected on day 0 and on day 3. Immediately after the end of experiment sheep were slaughtered. Parts of the brains were fixed in situ for further immunohistochemical analysis, while the remaining brains were frozen for Real Time RT-qPCR analysis. Substantial changes in the activity of the somatotrophic axis were observed in obestatin-infused sheep. In those animals obestatin evoked an increase in growth hormone-releasing hormone (GHRH) mRNA expression and a decrease in somatostatin mRNA expression in the anterior hypothalamic area. Moreover, a decrease in somatostatin immunoreactivity in the periventricular nucleus and an increase in somatostatin immunopositive fibers in the median eminence were noted. Changes in the GHRH and somatostatin activity are associated with an increase in growth hormone (GH) gene expression and in the amount of GH immunoreactive material stored in the somatotrophic pituitary cells. Consequently, an increase in GH concentration in the peripheral blood, due to an increase in the number of pulses was observed. It was revealed that obestatin affects the somatostatin/GHRH/GH system at the level of protein synthesis, accumulation and release. It is suggested that obestatin participates in the mechanism modulating somatotrophic axis activity at the central level by stimulating GH release through suppression of somatostatin output. Thereby, it can be concluded that obestatin may be involved in the modulation of growth processes in sheep. [ABSTRACT FROM AUTHOR]