VIP inhibits CCK-induced gallbladder contraction involving a beta-adrenoceptor mediated pathway in the rainbow trout, Oncorhynchus mykiss, in vivo.

The effects of VIP on CCK-induced contractions of the gallbladder were studied in the rainbow trout, Oncorhynchus mykiss, in vivo. Gallbladder pressures were measured via a catheter inserted into the gallbladder, and drugs were injected through a catheter in the dorsal aorta. CCK-induced contractions of the gallbladder wall were reduced in a dose-dependent manner by VIP. The effect of VIP was inhibited by the beta-adrenergic antagonist sotalol, indicating an adrenergic link in the VIP inhibition of the CCK-induced contraction. It is suggested that activation of VIP nerves could facilitate postprandial filling/refilling of the gallbladder despite the increased plasma levels of CCK during this period.