We have shown that 7 days of fetal hypoxemia due to uterine blood flow (Ut BF) reduction results in a decrease in fetal growth rate without any affect on fetal O2 consumption (AJP,1996). We hypothesized that under conditions of reduced O2 delivery to the fetus, O2 consumption is maintained by downregulation of energy expensive metabolic processes related to growth, specifically by a decrease in protein turnover. To test this hypothesis we studied 14 late gestation fetal sheep before and after 7 days of Ut BF reduction. To control for the affect of advancing gestational age, 4 sheep that were similarly prepared, but that did not undergo Ut BF reduction, were also studied. Fetoplacental leucine (Leu) rate of appearance (Ra) was calculated from an infusion of [1-13C]Leu with reciprocal pool modeling. The fraction of Leu Ra oxidized (Ox) was calculated from an infusion of[1-14C]Leu. Results (mean ± SEM) from the Ut BF reduction sheep are shown in the table. [O2] is mM; other data areμmol/min. *p<0.05 In control sheep, there were no significant differences from the Basal to the Day 7 study for fetal O2 delivery, Leu uptake, Leu oxidation rate, or fetoplacental Leu Ra. We conclude that 7 days of Ut BF reduction results in: 1) Decreased fetal O2 delivery and hypoxemia without decreased O2 consumption. 2) Significant reduction in fetoplacental protein turnover as reflected by the 20% decrease in Leu Ra. 3) A 25% decrease in fetal Leu Ox. We speculate that the decrease in protein turnover represents a substantial savings in fetal energy expenditure that allows the fetus to maintain its O2 consumption rate, in spite of a significant reduction in O2 delivery. Furthermore, this decrease in fetoplacental protein turnover may be influential in reducing fetal growth during prolonged Ut BF reduction.
