Timing of maternal nutrient restriction during mid- to late-gestation influences net umbilical uptake of glucose and amino acids in adolescent sheep

Previous research demonstrated that maternal nutrient restriction during mid- to late-gestation influenced net umbilical uptakes of glucose and amino acids in sheep. However, it is unclear how the timing and duration of nutrient restriction during mid- to late-gestation influences net uterine, uteroplacental, and fetal flux of glucose and amino acids. On day 50 of gestation, 41 adolescent ewe lambs carrying singletons were randomly assigned to one of six dietary treatments: 1) 100% of nutrient requirements from days 50 to 90 of gestation (CON; n = 7); 2) 60% of nutrient requirements (RES; n = 7) from days 50 to 90 of gestation; 3) 100% of nutrient requirements from days 50 to 130 of gestation (CON-CON; n = 6); 4) 100% of nutrient requirements from days 50 to 90 of gestation and 60% of nutrient requirements from days 90 to 130 of gestation (CON-RES; n = 7); 5) 60% of nutrient requirements from days 50 to 90 of gestation and 100% of nutrient requirements from days 90 to 130 of gestation (RES-CON; n = 7); or 6) 60% of nutrient requirements from days 50 to 130 of gestation (RES-RES; n = 7). On day 90 (n = 14) and day 130 (n = 27), intraoperative procedures were performed to evaluate uteroplacental blood flows, collect blood samples, and then ewes were euthanized. Net uterine, uteroplacental, and umbilical fluxes of glucose and amino acids were calculated by multiplying blood flow by the arterial-venous concentration difference. Data from days 90 and 130 were analyzed separately using ANOVA in SAS. Maternal nutrient restriction during mid-gestation increased (P = 0.04) net umbilical glucose uptake but, maternal nutrient restriction during late-gestation decreased (P = 0.02) net umbilical glucose uptake. Net umbilical essential amino acid uptake decreased (P = 0.03) with nutrient restriction during mid-gestation; however, net umbilical uptakes of Phe (P = 0.02), Thr (P = 0.05), Met (P = 0.09), and His (P = 0.08) increased or tended to increase after nutrient restriction during late-gestation. These data demonstrate that net umbilical glucose and amino acid uptakes were influenced by the timing of nutrient restriction during mid- to late-gestation. Elevated net umbilical glucose uptake after mid-gestational nutrient restriction was sustained throughout late-gestation, independent of late-gestational feeding level. Long-term adaptations in umbilical glucose uptake may have implications for prenatal and postnatal growth and development of the offspring. Mid-gestational vs. late-gestational nutrient restriction can alter patterns of net umbilical uptake of glucose and amino acids in sheep. Maternal undernutrition during gestation can lead to decreased fetal growth, decreased uteroplacental blood flow, and changes in nutrient supply to the fetus. However, it is unclear how the timing (mid-gestation vs. late-gestation) and duration (40 d vs. 80 d) of nutrient restriction influence nutrient supply to the fetus during mid- to late-gestation. Pregnant ewe lambs fed a pelleted diet to meet 100% of nutritional requirements or 60% of nutritional requirements during mid-gestation alone (days 50 to 90) or during mid- and late-gestation (days 50 to 130). At the end of mid-gestation and late-gestation, the net nutrient supply between the maternal, placental, and fetal compartments was measured. The results indicated that the timing of nutrient restriction influenced the net nutrient supply to the fetus but, the duration of nutrient restriction did not. Nutrient restriction during mid-gestation increased glucose to the fetus but nutrient restriction during late-gestation decreased glucose to the fetus. The opposite response occurred for fetal essential amino acid supply where nutrient restriction during mid-gestation decreased essential amino acid supply to the fetus but increased for several essential amino acids during late-gestational nutrient restriction. The timing of maternal undernutrition during mid- to late-gestation can affect the amount of nutrients delivered to the fetus and thus, could potentially impact postnatal growth and development.