Initially more rapid small intestinal glucose delivery increases plasma insulin, GIP, and GLP-1 but does not improve overall glycemia in healthy subjects

The rate of gastric emptying of glucose- containing liquids is a major determinant of postprandial glycemia. The latter is also dependent on stimulation of insulin secretion by glucose- dependent insulinotropic polypeptide ( GIP) and glucagon- like peptide- 1 ( GLP- 1). Although overall emptying of glucose approximates 1 - 3 kcal/ min, the " early phase" of gastric emptying is usually more rapid. We have evaluated the hypothesis that increased stimulation of incretin hormones and insulin by a more rapid initial rate of small intestinal glucose delivery would reduce the overall glycemic response to a standardized enteral glucose load. Twelve healthy subjects were studied on two separate days in which they received an intraduodenal ( id) glucose infusion for 120 min. On one day, the infusion rate was variable, being more rapid ( 6 kcal/ min) between t = 0 and 10 min and slower ( 0.55 kcal/ min) between t = 10 and 120 min, whereas on the other day the rate was constant ( 1 kcal/ min) from t = 0 - 120 min, i. e., on both days 120 kcal were given. Between t = 0 and 75 min, plasma insulin, GIP, and GLP- 1 were higher with the variable infusion. Despite the increase in insulin and incretin hormones, blood glucose levels were also higher. Between t = 75 and 180 min, blood glucose and plasma insulin were lower with the variable infusion. There was no difference in the area under the curve 0 - 180 min for blood glucose. We conclude that stimulation of incretin hormone and insulin release by a more rapid initial rate of id glucose delivery does not lead to an overall reduction in glycemia in healthy subjects.