Arteriovenous differences across the leg and across the splanchnic bed were determined for plasma glutamine and glutamate in healthy controls and insulin-dependent diabetics. In both groups glutamine was released from the leg and taken up by the splanchnic bed, while the reverse was observed for glutamate. Arterial glutamine levels were reduced by 25 per cent in the diabetics, but no differences were observed between the diabetics and controls in splanchnic or peripheral glutamine and glutamate metabolism. To assess the contribution of intestinal tissues to splanchnic glutamine uptake, arterio-portal venous differences (A-PV) were determined for plasma glutamine in four nondiabetic patients prior to elective cholecystectomy. A consistently positive A-PV difference was noted indicating net uptake of glutamine by intestinal tissues.
The findings indicate that the intestinal tract rather than the liver is the major site of splanchnic glutamine uptake and that removal of glutamine by the splanchnic bed is not augmented in diabetes. The data thus suggest that glutamine is not an important endogenous substrate for hepatic gluconeogenesis.