A UNIQUE RECEPTOR-MEDIATED MECHANISM IN VAGAL CHEMORECEPTION OF SOMATOSTATIN IN THE HEPATOPORTAL AREA

Our previous results have indicated that the hepatic vagus is receptive to intraportal appearance of somatostatin-14 (SS), a gastroenteropancreatic Peptide hormone, in rat. To examine the actual involvement of the SS receptor mechanism in the neural reception, the receptor function was modified with monoclonal antibody against rat neural SS receptor. Our monoclonal antibody of IgG1(kappa) isotype bound to the SS binding site of the receptor in competition with the ligand. Intraportal SS injection at a physiological dose (3.05 pmol) significantly facilitated the afferent firing discharge rate of the hepatic vagus in rats anesthetized with urethane and chloralose. The antibody ascites, but not the control ascites, administered intraportally 5 min prior to the SS injection abolished completely the SS-induced increase in discharge rate. However, when the antibody was administered more than 15 min after the SS injection, the SS-induced increase in discharge rate did appear, implying an unique post-receptor mechanism in reception. The present results indicate that the SS receptor mechanism operates in the neurochemoreception of SS, suggesting the existence of a hepatic vagal, receptor-mediated system for monitoring the hormone secreted from the splanchnic organs.