Release of immunoreactive vasoactive intestinal peptide (VIP) from the gallbladder in response to vagal stimulation

Immunoreactive VIP was detected in the gallbladder lumen and in the arterial blood and venous effluent from the gallbladder in fasting cats. During perfusion of the gallbladder in vivo there was a constant basal intraluminal secretion of VIP. The VIP concentration in the luminal effluent exceeded that in plasma supporting the notion that there was a release from the gallbladder tissue. The rate of secretion was significantly increased during efferent electrical stimulation of the peripheral cut end of the cervical vagal nerves, after blockade with atropine. A similar increase in concentration of VIP was seen in the venous effluent from the gallbladder. The results suggest a local release of VIP from intrinsic neurons within the gallbladder wall. This release is increased in response to activation of non-cholinergic fibres in the vagus nerves, suggesting a role for VIP in regulation of gallbladder functions.