Effectiveness of the intestinal polypeptides, IRP, GIP, VIP and motilin on insulin release in the rat

Intestinal insulin releasing polypeptide (IRP) and Gastric inhibitory polypeptide (GIP) have a similar effect on intravenous glucose tolerance in the rat. Both augment the insulin response to intravenous glucose and increase the rate of glucose disappearance. VIP and motilin have no discernible effect. Plasma insulin dose-response curves to IRP and GIP are similar; both peptides stimulate insulin release in the presence of small blood glucose increments. A direct comparison of the insulin releasing potency of IRP and GIP is not possible as the former is not yet available in pure form.