Clinical studies with gastric inhibitory polypeptide.

Intravenous infusion of porcine GIP in man induces insulin release when a degree of hyperglycemia is present. This glucose-dependent insulinotropic response occurs when a dose of GIP is administered to obtain circulating levels of approximately 1 ng/ml, a physiologic level that can be achieved by the ingestion of glucose or corn oil or a mixed meal. Serum GIP was measured by radioimmunoassay, and the single antiserum used in all the described studies measures 2 immunoreactive forms of GIP. In patients with chronic pancreatitis receiving an oral glucose load or mixed liquid test meal, GIP levels have been shown to be exaggerated. Similar elevated responses have been observed in obese patients and in maturity onset diabetes. A reduced GIP response has been seen in patients with celiac disease. A physiologic role for GIP in the enteroinsular axis has been established. However, involvement of the hormone in pathophysiologic situations is equivocal.