Maternal Nutrient Restriction During Midgestation Decreases Uteroplacental Release and Fetal Uptake of Essential Amino Acids in Sheep.

To examine the effects of maternal nutrient restriction on net uteroplacental flux during mid-gestation, 14 singleton ewes (48.2 ± 4.0 kg body weight) were fed 100% (control; CON; n = 7) or 60% of nutrient requirements (restricted; RES; n = 7) from day 50-90 (mid-gestation). On day 90, uteroplacental blood flow was measured via Doppler ultrasonography and blood samples were collected from the femoral artery, uterine vein, umbilical artery, and umbilical vein. Blood vessel glucose and amino acids (AA) concentrations were measured and arterial-venous (uterine, AV; fetal, va) differences and net fluxes were calculated. Data were analyzed using the GLM procedure of SAS for effects of treatment. Nutrient restriction during mid-gestation did not influence (P ≥ 0.17) uterine or umbilical blood flows. Uterine AV and fetal va differences of total, essential, and nonessential AA were not influenced (P > 0.10) by nutrient restriction. Nutrient restriction decreased (P ≤ 0.05) uterine and uteroplacental release of total AA and tended to decrease (P = 0.07) total AA uptake by the fetus. Uteroplacental release and fetal uptake of essential AA were decreased (P = 0.03) with RES by 53.4% and 45%, respectively. Uterine and uteroplacental release of nonessential AA were decreased (P = 0.03) with RES but, fetal uptake was not affected (P = 0.14). Nutrient restriction decreased (P ≤ 0.04) fetal uptake of methionine, phenylalanine, threonine, and valine and tended to decrease (P ≤ 0.10) fetal uptake of isoleucine, leucine, and tryptophan. Umbilical artery glucose concentrations were 32% lesser (P = 0.01) with RES and RES tended to increase (P = 0.08) fetal glucose uptake. Nutrient restriction during mid-gestation altered uteroplacental and fetal flux of AA in the current study. The results may indicate that fetal metabolism shifts to adapt to reduced AA supply which results in greater glucose utilization. [ABSTRACT FROM AUTHOR]