GLUCOSE AND L-LACTATE METABOLISM IN PREGNANT AND IN LACTATING EWES FED BARLEY-BASED OR GROUND MAIZE-BASED DIETS

The contribution of glucose absorbed from the small intestine to whole -body glucose metabolism was examined in ewes during late pregnancy an d early lactation, using diets based on ground barley or ground maize. Glucose and L-lactate turnover in the whole body and the mesenteric-d rained viscera were investigated in these ewes using isotope dilution techniques. The net absorption of glucose by the mesenteric-drained vi scera and whole-body glucose turnover were unaffected by diet or repro ductive status. Arterial and mesenteric venous blood glucose concentra tions, arterial and mesenteric venous L-lactate concentrations and who le-body lactate turnover were all significantly higher in lactation th an in pregnancy. The whole-body rates of lactate conversion to glucose and to other products were significantly higher in lactation than in pregnancy. Using a two-pool model of whole-body glucose and lactate me tabolism, a relatively high percentage of glucose was converted to lac tate (64-84%), accounting for 60-80% of whole-body lactate turnover. A model of glucose and lactate metabolism by the mesenteric-drained vis cera was constructed. Both the calculated endogenous glucose productio n and the visceral conversion of glucose to lactate were greater in la ctation than in pregnancy when barley was fed. Calculated total glucos e absorption was relatively constant, contributing between 26 and 59% of whole-body glucose turnover. Diet had little effect on glucose and lactate metabolism in either the mesenteric-drained viscera or the who le-body of breeding ewes.