Effects of porcine intestinal heptacosapeptide and vasoactive intestinal polypeptide on insulin and glucagon secretion in rats.

Pure porcine vasoactive intestinal polypeptide (VIP) and porcine intestinal heptacosapeptide (PHI) were infused in fed rats in doses of 1, 10, and 100 pmol/kg . min. The peptides were administered alone or together with glucose (40 mg/kg . min) or arginine (50 mg/kg . min). In the basal state, VIP at a dose of 1 pmol/kg . min and PHI at a dose of 10 pmol/kg . min produced a slight but significant hypoglycemia, whereas 100 pmol/kg . min VIP and PHI had a hyperglycemic effect. VIP at a dose of 10 and 100 pmol/kg . min enhanced the glucose-induced secretion of insulin. PHI exerted such an effect only when administered at the highest dose. When arginine was present as a secretagogue, 10 pmol/kg . min of both VIP and PHI potentiated secretion of insulin and glucagon and elevated the prevailing hyperglycemia. In conclusion, when given as a constant infusion in rats, both PHI and VIP exert a direct hypoglycemic effect and modulate the influence of glucose and arginine on insulin and glucagon secretion. It is as yet unclear to what extent these findings reflect normal physiological events.