Effects of intraduodenal nutrient infusion on insulin response to subsequent intravenous glucose in rats.

To elucidate the so-called incretin effect, the effects of intraduodenal bolus injection of glucose, 0.9% NaCl (saline), amino acids, and triglyceride on insulin response to subsequent intravenous injection of glucose (0.5 g/kg in 10% solution) was investigated in rats. Portal and femoral venous insulin and glucose concentration were simultaneously measured. Significantly higher portal insulin and lower femoral glucose values were observed in intraduodenal glucose or saline injection rats compared with controls (nothing was infused into the duodenum). Peripheral removal of insulin in these rats was not decreased. In the rats with intraduodenal injection of amino acids or triglyceride, slightly higher portal insulin and lower femoral glucose values were observed, but they were not significantly different from controls. These results indicate that incretin effect is provoked by intraduodenal infusion of glucose and saline, and may have some important physiologic role on glucose metabolism in rats in vivo.