Effects of Porcine Intestinal Heptacosapeptide and Vasoactive Intestinal Polypeptide on Insulin and Glucagon Secretion in Rats*

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Abstract
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. Thepeptides were administered alone or together with glucose (40 mg/kg-min) or arginine (50 mg/kg-min). In the basal state, IP 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 glucoseinduced 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.