Glucose and Lactate Oxidation Rates in the Fetal Lamb

TLDR

Glucose and lactate are key fetal nutrients that can serve as fuels for oxidation or as carbon sources for energy storage and tissue accretion. The study reports in vivo oxidation rates of glucose and lactate in fetal lambs over a short period. The oxidation fraction was calculated as the ratio of 14CO2 excretion across the umbilical circulation to the net entry of [14C]glucose or [14C]lactate into fetal tissues. Glucose oxidation averaged 61.2 % (2.55 mg min⁻¹ kg⁻¹) and accounted for 28 % of oxygen uptake, while lactate oxidation averaged 71.5 % (4.12 mg min⁻¹ kg⁻¹); both fractions increased with fetal blood concentrations, indicating preferential oxidation of glucose and lactate over other fuels.

Abstract

Both glucose and lactate are nutrients of the ovine fetus. Each may be used by the fetus as a fuel for oxidation or as a source of carbon for energy storage and net tissue accretion. The present report describes the oxidation rates of glucose and lactate in vivo for the fetal lamb over a relatively short time period. The fraction of fetal glucose or lactate oxidized was defined as the ratio of 14CO2 excretion across the umbilical circulation to the net entry of [14C]glucose or [14C]lactate into fetal tissues. The fraction of glucose oxidized over a 3-hr study averaged 61.2%, accounting for 2.55 mg · min-1 · kg-1 of glucose oxidized and for 28% of the simultaneous net oxygen uptake. The fraction of lactate oxidized averaged 71.5%, accounting for 4.12 mg·min-1 · kg-1 of lactate oxidized. Oxidation fractions and rates for both glucose and lactate increased with their concentrations in fetal blood suggesting sparing of other fuels for oxidation at higher glucose and lactate concentrations.