INVOLVEMENT OF VASOACTIVE INTESTINAL POLYPEPTIDE IN GASTRIC REFLEX RELAXATION

We have previously presented evidence for a non-adrenergic, vagally me diated colono-gastric inhibitory reflex induced by distension of the c olon. We also found that pain stimulation by putting pressure on a tes ticle induced a pronounced gastric relaxation mediated by both adrener gic and vagal non-adrenergic fibres in anesthetized rats. Previous in vitro studies by other workers have strongly indicated that vasoactive intestinal polypeptide (VIP) is a neural mediator of gastric relaxati on. The aim of the present in vivo study was to investigate, in anesth etized rats, whether VIP is involved in the gastric reflex relaxation induced by colonic distension and pain stimulation. A volumetric metho d was used to monitor changes in gastric volume. Gastric reflex relaxa tion following colonic distension was significantly and markedly inhib ited by VIP antiserum as compared to the control relaxation before adm inistration of the antiserum. Non-immunized control serum did not sign ificantly influence gastric relaxation caused by colonic distension. P ain-induced gastric relaxation was moderately but significantly reduce d after the administration of VIP antiserum but not after control seru m. The selective beta2-adrenoceptor agonist, salbutamol, induced a pro nounced gastric relaxation of the same magnitude before and after the administration of VIP antiserum. VIP antiserum changed the pattern of gastric motility by inducing a specific type of gastric contraction ap pearing spontaneously or in response to colonic distension. A close in tra-arterial injection of VIP induced gastric relaxation and inhibitio n of phasic gastric contractions. The present results in the rat sugge st that VIP or a VIP-like peptide is involved in gastric reflex relaxa tion induced by colonic distension and pain stimulation.