In Vivo: GLP-1(7-37) (0.5, 5 or 50 pmol/min/kg) infused during the second hour of a 2-hour 11-mM hyperglycemic clamp produces a dose-related enhancement of the glucose-stimulated increase in plasma insulin concentration and an increased rate of glucose infusion in rats. Infusion of GLP-1(7-37) (5 pmol/min/kg) from 1 hour through 7 hours produces a sustained increase in plasma insulin concentration relative to levels in rats infused with vehicle in rats with maintained glucose concentration at 11 mM.