Role of selected peptides in the vagal regulation of gastric motor and endocrine pancreatic function

The dorsal vagal complex (DVC) and nucleus raphe obscurus (nROb) are currently known to control vagal outflow to the stomach and the pancreas. Elucidation of neurotransmitters in these nuclei that control vagal outflow has become necessary to determine the endogenous circuitry for control of gastric motor activity and pancreatic hormone secretion. In this review, the author's data on the effects of selected peptides on intragastric pressure and gastric contractility as well as on pancreatic glucagon and insulin secretion in the DVC and nROb are presented. Microinjection of thyrotropin-releasing hormone (TRH) or pituitary adenylate cyclase-activating polypeptide (PACAP38) into the nROb results in gastric excitatory motor responses, whereas substance P (SP) and vasoactive intestinal polypeptide (VIP) evoke gastric relaxation. Irrespective of colocalization of TRH and SP in the serotonergic neurons of the nROb, these peptides independently affect gastric motor function when microinjected into the nROb. The inhibitory effect of SP on gastric motor function in the nROb is apparently mediated via nitric oxide in the DVC and involves peripheral VIP, acetylcholine, gamma-aminobutyric acid and nitric oxide. Microinjection of endothelin, PACAP38, and VIP into the DVC evokes increases in gastric motor activity. Pancreatic polypeptide, microinjected into the potentiates glucose-stimulated insulin secretion. All these data make an important contribution to our understanding of the vagal mechanisms controlling gastric motor and endocrine pancreatic function.