Effects of hexamethonium and atropine on the basal levels of immunoreactive vasoactive intestinal polypeptide in dogs.

The basal levels of immunoreactive vasoactive intestinal polypeptide (IR-VIP) in veins of the gastrointestinal tract and the effect of hexamethonium and atropine on basal levels of IR-VIP were examined in anesthetized dogs. The basal mean plasma IR-VIP levels in the pancreaticoduodenal vein, the mesenteric vein of the jejunum, the mesenteric vein of the ileum and the right colonic vein, but not the left gastroepiploic vein, were significantly higher than those in the femoral vein. These basal levels of IR-VIP were decreased by atropine, but not by hexamethonium. Thus, the main source of basal VIP in the portal vein is probably the duodenum (and pancreas) and the small and large intestine, and the basal levels of VIP are under the control of muscarinic receptors, in canine gastrointestinal tract.