Thyroid hormone metabolism in amniotic and allantoic fluids of the sheep.

Amniotic and allantoic fluid samples were obtained at the time of uterotomy from healthy pregnant ewes at various time during gestation. In most instances maternal and fetal blood was collected simultaneously. Serum thyroxine (T4) and triiodithyronine (T3) and free T4 were measured in most samples. To determine whether conjugastes of T4 were presented in amniotic and allantoic fluids. T4 was measured before and after 24-hr acid hydrolysis. T4 and T3 turnover from amniotic fluid were measured using kinetic methods after intravenous or intraamniotic fluid injection of radiolabeled hormones. T3 was unmeasurable less than 15 ng/100 ml) in amniotic and allantoic fluids as well as in most fetal serum samples. T4 levels in amniotic fluids were low before 120 days of gestation (0.17 +/- 0.03 mug/100 ml; mean and SEM) concentration between 124 and 152 days was 0.33 +/- 0.03 mug/100 ml. T4 concentrations in allantoic fluid were relatively high before 120 days (0.57 +/- 0.1 mug/100 ml) and did not increase with progression of the pregnancy...