Differential effects of subcutaneous GLP-1 on gastric emptying, antroduodenal motility, and pancreatic function in men.

In this study of eight healthy male volunteers, we investigated the effects of graded doses of subcutaneous glucagon like peptide-1(7-36)amide (GLP-1) on: 1) the gastric emptying pattern of a mixed liquid meal (300 kcal); 2) pancreatic enzyme secretion; 3) antroduodenal motility; and 4) the glycemic response as well as releases of insulin, C-peptide, and glucagon. GLP-1, 0.125 nmol/kg, or 0.25 nmol/kg, or placebo was injected subcutaneously 5 min before meal ingestion. Subcutaneous GLP-1 dose-dependently prolonged the lag period (i.e., the time to reach maximal velocity of gastric emptying) by 46.2% (low dose) and 93.7% (high dose) (p < .05) but left unaltered maximal emptying velocity, total emptying time, and exponential emptying rate. With and without GLP-1, a fed motor pattern was induced by the meal and was terminated by an antral phase III when 98% of the meal had emptied. In parallel to the prolonged lag period, GLP-1 dose-dependently inhibited antral and duodenal motility and coordinated antroduodenal contractions by > 50% (low dose) and > 70% (high dose) (p < .05). GLP-1 initially reduced and thereafter transiently stimulated pancreatic enzyme secretion. This pattern correlated with the prolonged lag period and mirrored the delayed gastric emptying. GLP-1 retarded and diminished the postprandial glucose peak and reduced the total plasma glucose response by 46.6% (low dose) and by 59.4% (high dose) (p < .05). Both doses of GLP-1 delayed the postprandial insulin peak, enhanced total insulin release, and diminished postprandial responses of glucagon and pancreatic polypeptide. The duration of the lag period strongly correlated with the timing of postprandial glucose and insulin peaks (p < .001). The initial delay of gastric emptying, the enhancement of postprandial insulin release, and the inhibition of postprandial glucagon release were independent determinants (p < .01-.05) of the postprandial glucose response after subcutaneous administration of GLP-1.