THE EFFECT OF THE INTESTINAL POLYPEPTIDES, IRP AND GIP, ON INSULIN|RELEASE AND GLUCOSE TOLERANCE IN THE BABOON

The recently isolated intestinal polypeptides, intestinal insulin releasing polypeptide (IRP) and gastric inhibitory polypeptide (GIP), have been shown to potentiate glucose stimulated insulin release in the baboon. The effect was similar to that seen in the rat and demonstrates that both peptides affect insulin release in a broad range of species. No effect on glucagon release was observed. The possibility that either IRP or GIP, or both, is involved in the alimentary augmentation of insulin release by oral glucose deserves consideration. It is now well recognized that intestinal hormones are concerned in the regulation of glucose homeostasis (McIntyre et al., 1964; Marks & Samols, 1970), but their absolute identity and relative importance is uncertain. Two recently isolated polypeptides, intestinal insulin releasing polypeptide (IRP) (Turner, 1972; Turner et al., 1973) and gastric inhibitory polypeptide (GIP) (Brown et al., 1969), have been shown to produce dramatic effects on the insulinaemic response to intravenous glucose in the rat (Turner et al., 1973; Dupre, 1973). In order to determine whether these effects are limited to the rat, or a general phenomenon, the ability of the two peptides to augment the insulin response to intravenous glucose was examined in the baboon, Papio papio. In view of the known suppressive effect of oral glucose on glucagon release, plasma glucagon levels were also measured.