Efffect of vasoactive intestinal polypeptide on gallbladder smooth muscle in vitro

The effect of vasoactive intestinal polypeptide (VIP) on basal and octapeptide of cholecystokinin (OP-CCK) induced tension was examined with guinea pig gallbladder smooth muscle strips in vitro. VIP alone produced dose-related decreases in resting tension and antagonized spontaneous contractile activity where present. In combination with OP-CCK, VIP decreased the expected contractile respone. The degree of antagonism depended upon the concentrations of OP-CCK and VIP. VIP had no effect on acetylcholine-induced contractions. From these observations, we propose that VIP can affect gallbladder motor activity by decreaseing smooth muscle tone and by antagonizing cholecystokinin. These findings lend further support to our proposal that gallbladder motor function may depend upon the action and interaction of the gastrointestinal hormones.