INTERACTIONS OF VIP (VASOACTIVE INTESTINAL POLYPEPTIDE) AND NITRIC-OXIDE (NO) IN MEDIATING INTESTINAL INHIBITION

In this review, the roles of VTP and NO as inhibitory mediators of non -adrenergic non-cholinergic inhibition of the gastrointestinal tract a re considered. In canine intestine and LES and opossum oesophagus, NO seems to be the primary mediator of membrane hyperpolarization and rel axation. In sphincters both NO and VIP may function independently to i nitiate the relaxation,In canine intestine, VIP apparently has no dire ct role to affect circular smooth muscle, but may play a neuromodulato ry role. In other tissues there may be interactions including neuromod ulation of release of VIP by NO and vice versa. Evidence that VIP may release NO from smooth muscle cells or interstitial cells of Cajal is considered critically. Recent controversy about the roles of VIP and N O are also noted and criteria for evaluating conflicting claims provid ed.