The effects of chronic fetal hyperglycemia on substrate uptake by the ovine fetus and conceptus.

Hyperglycemia in fetal sheep has been shown to increase the fetal metabolic rate. Fetal venous glucose infusion was performed in eight late gestation, chronically catheterized fetal lambs to assess any changes in substrate uptake by the ovine uterus and conceptus. Fetal glucose infusion (11.9 +/- 0.6 mg glucose X kg-1 X min-1) caused a stable increase in fetal plasma glucose concentration approximately 3-fold above baseline. The fetal glucose entry rate increased from 6.6 +/- 0.7 to 9.3 +/- 0.6 mg X kg-1 X min-1 by day 3 of infusion (p less than 0.01) despite a net umbilical glucose excretion during the period of fetal hyperglycemia. Due to a concomitant increase in fetal oxygen consumption, no change in fetal glucose/O2 quotient was observed. A significant relationship was noted (p less than 0.02) between the fetal glucose entry rate and the rate of fetal oxygen consumption. Fetal glucose infusion caused a decrease in uterine glucose uptake as well. No changes were observed in calculated net placental glucose uptake although the relative fetal contribution increased from net placental exit to fetus to a placental uptake amounting to 20.8 +/- 5.8% of the total placental glucose uptake (p less than 0.01). Although no changes in fetal lactate concentration occurred, both maternal and fetal lactate entry rates increased, the magnitude of increase being significantly related to fetal glucose concentration. Both maternal and fetal insulin concentrations rose during the period of fetal hyperglycemia and were related to the respective increases of maternal or fetal substrate uptakes but not to fetal oxygen consumption.(ABSTRACT TRUNCATED AT 250 WORDS)