Preceding hyperinsulinemia prevents demonstration of insulin effect on fat-induced gastric inhibitory polypeptide (GIP)
1984
Stockmann, F. | Ebert, R. | Creutzfeldt, W.
Extract: The effect of insulin on fat-induced gastric inhibitory polypeptide (GIP) release has been studied in seven healthy volunteers during euglycemic blood glucose clamping. In the first protocol, insulin (0.1 units per kilogram per hour) was infused 2 hours before ingestion of 100g fat and continued for 2 hours thereafter. In protocol II, saline was infused 2 hours before the fat load and the insulin infusion started at the time of fat ingestion. During both insulin infusion studies, glucose levels were clamped at the fasting level by means of the Biostator and plasma levels of insulin, C-peptide, and GIP were estimated by radioimmunoassay. The response of GIP to oral fat was inhibited by 63% if insulin infusion was started at the time of fat ingestion, whereas no inhibition was seen if a 2-h hyperinsulinemic period preceded the fat load. The plasma insulin levels were comparable at the end of each experiment, ranging from 110 to 130 microgram units per mililiters. Plasma C-peptide levels decreased during the insulin infusion and increased after fat ingestion. These findings were not the result of inhibition of gastric emptying by insulin because they could be confirmed in four volunteers with intraduodenal infusion of fat. The present data show that insulin does inhibit fat-induced GIP secretion in normal man, but preceding hyperinsulinemic glucose clamping masks this insulin effect, probably by decreasing the sensitivity of the GIP cells to insulin. (author)
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