Evidence in vivo that most of the intraluminally absorbed glucose is absorbed intact into the portal vein and not metabolized to lactate.

Studies in vitro and acute studies in vivo have indicated that the intestine may be a significant producer of portal-venous lactate, a major carbon source for liver glycogen synthesis. To determine if a significant portion of intraluminal glucose is converted into lactate by the intestine in vivo, we measured the ratio of intraluminal glucose which is absorbed intact into the portal vein to that which is converted into lactate by the intestine in a chronically catheterized rat, in which catheters were surgically placed into the portal vein, aorta and stomach. This ratio was 36-42 when intraluminal [U-14C]glucose concentrations of 5-200 mM were used, suggesting that the intestine may not be a significant source of portal-venous lactate in vivo. Under hypoxic conditions [PaO2 less than 40 Torr (5.3 kPa)] the ratio decreased to 2.1, indicating that the amount of intraluminal glucose converted into lactate had increased significantly.