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.