Comparative Effects of Synthetic and Natural Vasoactive Intestinal Peptide on Pancreatic and Biliary Secretion and on Glucose and Insulin Blood Levels in the Dog

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Abstract
The effects of synetic porcine vasoactive intestinal peptide (VIP) on pancreatic and biliary secretion and on glucose, insulin and calcium blood levels were examined in the dog and compared with the effects of natural porcine VIP. Synthetic VIP was a secretin-like partial agonist of pancreatic and biliary secretion with efficacies relative to secretin of 0.27 and 0.41, respectively. Consistent with its weak secretin-like action, synthetic VIP augmented the pancreatic response to CCK-OP and the submaximal but not the maximal response to secretin. Synthetic VIP also produced a dose-dependent increase in blood glucose levels and a synchronous and proportionate increase in blood insulin levels. A slight increase in total calcium levels was equivocal. The effects of natural VIP on pancreatic and biliary secretion and on glucose and insulin blood levels were identical to those of synthetic VIP. The identity of effects supports the validity of the postulated structure of porcine VIP. Although elicited at high doses, the effects of VIP on exocrine and endocrine secretion may be relevant physiologically in the context of a neurocrine or paracrine role for VIP.