Fetomaternal production and transfer of progesterone and uridine in sheep

Abstract

Catheters were placed in maternal and fetal vessels in sheep at advanced gestational ages. Blood samples were taken to determine concentrations of progesterone and uridine, with gauging of the fetal condition by measuring pH and blood pressure. Tritium and 14C-labeled progesterone and uridine were infused at a constant rate into fetal and maternal circulations to determine metabolic clearance rates and rates of production and fetomaternal transfer of these compounds. It was found that only 70 per cent of the labeled progesterone infused into an umbilical vein reached the fetal inferior vena cava. Since the fetal hepatic extraction of progesterone was estimated to be about 0.70, it was calculated that approximately 60 per cent of the fetal placental flow was shunted through the ductus venosus. Progesterone was found to be secreted by the placenta to the maternal circulation and only minimally to the fetus, although significant amounts of progesterone are transferred from mother to fetus. Large amounts of uridine were found to be released into fetal and maternal circulations and to be rapidly metabolized. Therefore, the low levels of circulating uridine do not reflect the potential importance of the nucleosides as precursors of nucleic acids. Concentrations in blood and metabolic clearance rates of both progesterone and uridine were found to be affected by the condition of the fetus.