CENTRAL SOMATOSTATIN PREVENTS VAGAL EFFERENT NERVE EXCITATION PRODUCED BY TRH BUT NOT BY 2-DEOXY-D-GLUCOSE

Thyrotropin-releasing hormone (TRH) administered intracerebroventricul arly and intravenous injection of 2-deoxy-D-glucose (2-DG) stimulate p ancreatic exocrine secretion via vagal efferent nerve excitation. We e xamined whether centrally administered somatostatin would inhibit panc reatic exocrine secretion that was stimulated by vagal efferent nerve excitation in conscious rats. The animals were prepared with cannulas draining bile and pancreatic juice separately and with a duodenal cann ula, a cerebroventricular cannula, and a right jugular vein cannula. I ntracerebroventricular injection of somatostatin (0.4 or 4 nmol) signi ficantly inhibited pancreatic secretion induced by TRH (50 or 500 pmol ) in a dose-dependent manner. Intravenous injection of somatostatin ha d no effect on pancreatic secretion stimulated by TRH. On the other ha nd, somatostatin injected centrally did not affect pancreatic secretio n induced by 2-DG (75 mg/kg) or basal secretion. These results suggest that TRH and 2-DG stimulate vagal efferent nerves via distinct mechan isms and that central somatostatin selectively inhibits excitation of the vagus induced by peptidergic (TRH) stimulation.