Effect of Maternal Glucose Concentration on Uteroplacental Glucose Consumption and Transfer in Pregnant Sheep

Abstract

The present study was designed to measure the relationships between maternal arterial glucose concentration ([GI]_A) and fetal arterial glucose concentration ([GI]_a), uteroplacental glucose consumption (UPGC), and the rate of uteroplacental glucose transfer to the fetus (UPGT) in pregnant sheep in late gestation. [GI]_A was controlled by a glucose clamp technique and the glucose flux rates of the uteroplacenta were quantified by the Fick principle. [GI]_A varied from 1.81 to 154.7 mg/dl; [GI]_a was directly related to [GI]_A: [GI]_a = 0.374 [GI]_A + 1.81, r = 0.873, P < 0.001. Fetal arterial blood oxygen content decreased with [GI]_A (P < 0.05) and fetal arterial blood lactate concentration increased with [GI]_A (P < 0.001). There was no significant effect of [GI]_A on the rates of uteroplacental lactate production, uteroplacental oxygen consumption, fetal oxygen consumption, or uterine or umbilical blood flow. Both UPGC and UPGT were directly related to [GI]_A: UPGC = −2.221 × 10^-3 χ ² + 0.646 × −6.016, r = 0.80; UPGT = −1.208 × 10^-3 χ ² + 0.405 × −2.416, r = 0.90. UPGC and UPGT were approximately parallel over the range of [GI]_A studied (UPGC = 1.19 UPGT + 3.79, r = 0.764). These results demonstrate the importance of UPGC to maternal-fetal glucose homeostasis and indicate that factors regulating uteroplacental glucose consumption and transfer to the fetus become limiting at comparable levels of [GI]_A and [GI]_a. The estimated kinetic constants for UPGC represent the metabolism of glucose by the uteroplacental tissues, but the estimated kinetic constants for UPGT represent the metabolism of glucose by the fetus as well as the transfer of glucose by the uteroplacenta to the fetus.