Identification and Actions of Gastric Inhibitory Polypeptide

This chapter gives an overview of the identification and actions of gastric inhibitory polypeptide (GIP). It describes an experiment in which it is concluded that exogenous or endogenous GIP is capable of insulinotropic effects in normal man and can lead to substantial acceleration of the disposal of glucose. Because GIP is released into the blood during absorption of glucose and that response is demonstrable on infusion of glucose directly into the intestine and after ingestion of glucose, this peptide is fully qualified to take part in the potentiation of insulin secretion after ingestion of glucose during absorption of glucose from the gut in normal man. The experiment findings clearly do not exclude the possibility that other humoral secretions of the intestine participate in the potentiation of insulin secretion under physiological conditions. However, the effects of apparently physiological doses of GIP strongly suggest that this agent is capable of accounting for a major part of the potentiation of insulin secretion attributed to humoral secretions of the intestine.