GLUCOSE AND [C-13]LEUCINE METABOLISM BY THE PORTAL-DRAINED VISCERA OFSHEEP FED ON DRIED GRASS WITH ACUTE INTRAVENOUS AND INTRADUODENAL INFUSIONS OF GLUCOSE

The effect of exogenous glucose supply by either intrajugular (IJG) or intraduodenal (IDG) infusion at 2.0 mg glucose/kg body weight per min was investigated in four wether sheep (average weight 44 (SD 4) kg) c hronically catheterized in the carotid artery and portal veins. Sheep were fed on a dried grass pellet diet hourly using continuous belt fee ders. Whole-body glucose irreversible loss (IL) rate, measured with [6 -H-3]glucose, was increased by 0.5 and 0.8 of exogenous supply for IJG and IDG infusions respectively. Portal glucose utilization, measured by isotope dilution across the portal-drained viscera, was unaffected by additional glucose regardless of the route of glucose supply (P=0.7 6 for control v. glucose infusions) and was a constant proportion of g lucose IL (0.28) for all treatments. Portal plasma flow was higher dur ing IDG infusions compared with IJG infusions (1.65 v. 1.44 litres/min , P=0.055). Circulating total free amino acid concentrations fell duri ng glucose infusions (2146, 1808 and 1683 mu mol/l for control, IJG an d IDG treatments respectively, P=0.067 for treatment effect) but net p ortal absorption was not affected by increased glucose supply. Recover y in the portal vein of [1-C-13]leucine infused into the duodenum aver aged 0.65 and was not affected by increasing glucose supply to the gut tissues. The results show that glucose utilization by gut tissues is responsive to changes in both vascular and luminal glucose supply. The effects of changing gut tissue use of glucose and increased whole bod y glucose IL on metabolism of nutrients is discussed.