Role of Nitric Oxide and Capsaicin-Sensitive Sensory Nerves in Gastric Receptive Relaxation and Adaptive Relaxation in Isolated Stomachs of Guinea Pigs

Abstract

We investigated the role of nitric oxide (NO) and capsaicin-sensitive sensory nerves (CPSNs) in gastric receptive relaxation and adaptive relaxation in isolated stomachs of guinea pigs. Changes in intragastric volume and pressure were recorded simultaneously in isolated stomachs in baths containing atropine and guanethidine. Receptive relaxation was induced by electrical vagal stimulation, and adaptive relaxation was induced by luminal distension. We found that receptive relaxation and adaptive relaxation were reduced by tetrodotoxin and N ^G-nitro-L-arginine (LNNA). The effect of LNNA was partially reversed by co-incubation with L-arginine. Hexamethonium inhibited receptive relaxation but not adaptive relaxation. Desensitization to capsaicin inhibited adaptive relaxation but not receptive relaxation. Extraluminal capsaicin induced gastric relaxation. Capsaicin-induced relaxation also was reduced by tetrodotoxin and LNNA but not by hexamethonium. Neither CGRP_(8–37), an antagonist of calcitonin gene-related peptide (CGRP) receptors, nor VIP_(10–28), an antagonist of vasoactive intestinal peptide (VIP) receptors, inhibited all responses of receptive relaxation and adaptive relaxation or capsaicin-induced relaxation. These findings suggest that NO, but not CGRP or VIP, may be involved in the mechanisms of receptive relaxation and adaptive relaxation, and that activation of CPSNs may be involved in adaptive relaxation.