Uterine blood flow and substrate uptake in conscious rabbit during late gestation

The aim of this study was the quantitation of the metabolic demands of the uterus in rabbits between days 24 and 30 of gestation, a time at which there is a fourfold increase in fetal weight. Serial measurements of substrate concentrations in maternal artery and uterine vein were performed over this period. Uterine blood flow was measured on days 24 and 30. Uterine substrate uptake was calculated by application of the Fick principle. Over the gestation range studied, the absolute uterine blood flow increased proportionally to the uterine weight gain. The uterine arteriovenous differences for glucose (G), lactate (L), free fatty acids (FFA), ketone bodies (KB), and oxygen (O2) were constant throughout the study. At both gestational ages, the weight-specific uterine substrate consumption (G, FFA, KB, O2) and production (L) were respectively similar. On days 24 and 30 the amount of G directed to the gravid uterus represented approximately 13 and approximately 36% of the maternal glucose turnover rate, respectively. The maximum contributions of G and FFA to the uterine oxygen consumption on day 24 were 80 and 30%, respectively. We have thus confirmed that at term the gravid uterus is a site of high glucose consumption. Finally, we demonstrated that in a nonruminant species, FFA would be a substantial source of carbon.