Evidence of local mechanism involvement in vasoactive intestinal polypeptide release from canine small intestine

We studied the effect of intraileal administration of a 100-ml test meal, 100 ml of 5% glucose, amino acids, 10% Intralipos, or bile on canine plasma immunoreactive vasoactive intestinal polypeptide (VIP) levels in the mesenteric and femoral veins of dogs. The effects of intravenous administration of caerulein on plasma immunoreactive VIP levels were examined, with or without intraduodenal ballooning, to rule out the effect of bile and pancreatic and gastric juice. In addition, hexamethonium bromide or atropine sulfate was given intravenously before the administration of bile or intravenous caerulein to study the role of the neural pathway on the release of VIP. Basal plasma VIP levels in the mesenteric vein were significantly higher than those in the femoral vein. Intraileal administration of the test meal, 5% glucose, amino acids, or 10% Intralipos induced no variation of mesenteric VIP. Intraileal administration of bile or intravenous caerulein, with or without intraduodenal ballooning, produced a significant increase of plasma VIP in the mesenteric vein. Pretreatment with atropine completely blocked the bile-stimulated VIP release and significantly inhibited the caerulein-stimulated release of VIP. On the other hand, pretreatment with hexamethonium did not significantly decrease the VIP response by bile or caerulein. Thus, the muscarinic receptor probably plays an important role in bile- or caerulein-stimulated release of VIP.