Physiological role of cholecystokinin on postprandial insulin secretion and gastric meal emptying in man. Studies with the cholecystokinin receptor antagonist loxiglumide

Summary Cholecystokinin was previously proposed to play an important role in the regulation of postprandial insulin secretion either indirectly, by inhibiting gastric meal emptying, or directly, by acting as an incretin promoting the release of insulin. The aim of this investigation was therefore to clarify the role of endogenous cholecystokinin in the regulation of insulin release and gastric emptying applying the highly potent and specific cholecystokinin receptor antagonist loxiglumide. Five healthy volunteers were examined after an overnight fast. Gastric meal emptying was measured by the double indicator technique using a multiple lumen tube in the duodenum and ^99mTc-diethylenetriamine pentaacetate as a meal marker and polyethylene glycol 4000 as a duodenal perfusion marker. Postprandial insulin, C-peptide, cholecystokinin and glucose levels were measured after ingestion of two isocaloric meals of a) Ensure (containing fat, protein and glucose), and b) a pure glucose meal (1.11 mol/l). The meals were given either with an intravenous infusion of loxiglumide (22 mol·kg^–1·h^–1) or placebo. The infusion of loxiglumide markedly accelerated the gastric emptying of the mixed meal (area under curve, 5576±352 min vs 3498±109 min; p<0.001) and the pure glucose meal (area under curve 5662±537 min vs 3551±534 min; p<0.05). Simultaneously, loxiglumide induced a more rapid rise in postprandial insulin levels after both meals resulting in significantly higher (p<0.05) insulin levels during the first postprandial hour, but similar insulin levels in the second postprandial hour. Accordingly, we found a close correlation between meal emptying and insulin release (r=0.748, p<0.01). Integrated insulin and C-peptide levels for the whole 2-h experimental period tended to be higher during loxiglumide infusion, but the difference did not reach statistical significance. Similar plasma glucose levels at all time periods were observed with and without loxiglumide infusion. Higher cholecystokinin levels were measured during loxiglumide infusion after the mixed (p<0.01) and the pure dextrose (p<0.05) meals. We conclude that postprandially released cholecystokinin exerts an important role in the regulation of gastric meal emptying and consecutively the postprandial pattern of insulin release. In contrast, no evidence was found for an insulinotropic role for cholecystokinin in man.