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

Our previous results have indicated that the hepatic vagus is receptiv e to intraportal appearance of somatostatin-14 (SS), a gastroenteropan creatic Peptide hormone, in rat. To examine the actual involvement of the SS receptor mechanism in the neural reception, the receptor functi on was modified with monoclonal antibody against rat neural SS recepto r. Our monoclonal antibody of IgG1(kappa) isotype bound to the SS bind ing site of the receptor in competition with the ligand. Intraportal S S injection at a physiological dose (3.05 pmol) significantly facilita ted the afferent firing discharge rate of the hepatic vagus in rats an esthetized 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 r ate. However, when the antibody was administered more than 15 min afte r the SS injection, the SS-induced increase in discharge rate did appe ar, implying an unique post-receptor mechanism in reception. The prese nt results indicate that the SS receptor mechanism operates in the neu rochemoreception of SS, suggesting the existence of a hepatic vagal, r eceptor-mediated system for monitoring the hormone secreted from the s planchnic organs.