Thyroid Hormone Metabolism in Amniotic and Allantoic Fluids of the Sheep

Abstract

ExtractAmniotic and allantoic fluid samples were obtained at the time o f uterotomy from healthy pregnant ewes at various times during gestation. I n most instances maternal and fetal blood was collected simultaneously. Serum thyroxine (T, and triiodithyronine (T, ) and free T, were measured in most samples. T o determine whether conjugates o f T, were present in amniotic and allantoic fluids. T, was measured before and after 24-hr acid hydrolysis. T, and T, turnover from amniotic fluid were measured using kinetic methods after intravenous or intraamniotic fluid injection o f radiolabeled hormones.T, was unmeasurable ( < 15 ng/100 m l ) i n amniotic and allantoic fluids as well as i n most fetal serum samples. T, levels in amniotic fluid were low before 120 days o f gestation (0.17 & 0.03 Leg/ 100 ml; mean and S E M ) and increased progressively thereafter to term. The mean (and S E M ) concentration between 124 and 152 days was 0.33 =t 0.03 pg/100 ml. T, concentrations in allantoic fluid were relatively high before 120 days (0.57 0.1 pg/lOO m l ) and did not increase with progression o f the pregnancy. There were no correlations between amniotic and allantoic fluid T, concentrations, between amniotic fluid T,, and either maternal or fetal serum T, levels. or between allantoic fluid T, and maternal or fetal serum T, at any time during gestation. Mean free T, concentrations were similar i n fetal serum and amniotic fluid and higher than values in maternal serum or allantoic fluid.Mean amniotic and allantoic fluid T, concentrations by radioimmunoassay ( R I A ) increased significantly after acid hydrolvsis, suggesting that one-third to one-half the T, in these fluids is present as T, conjugate.Radiolabeled T, or T, was injected into amniotic fluid and recovery o f hormone label was measured in serum and tissues at 24 hr for comparison with recoveries after intravenous injection. Mean T, radioactivity i n several organs or tissues was nearly identical whether the hormone was injected intravenously or into amniotic fluid. I n addition, the total residual labeled T, or T, in the fetal sheep (percentage dose per fetus) at the time of killing was similar after intravenous and intra-amniotic fluid injection. Chromatograms o f butanol-ammonia extracts o f fetal sera after intraamniotic or intravenous injection o f labeled T, were similar and showed predominantly T,; a significant iodide peak was observed as well as a small peak o f radioactivity with an R, corresponding to that of T, conjugate.The results indicate that there are low but measurable concentrations o f T, in amniotic and allantoic fluids of pregnant sheep. There appears t o be minimal exchange o f hormone between allantoic and amniotic fluid. Amniotic fluid T, levels, in contrast to allantoic fluid concentrations, increase progressively during the last half o f gestation. Although free T, concentrations are similar in amniotic fluid and i n fetal serum, and are higher than i n allantoic fluid o r maternal serum, the lack of correlation between T, levels i ...

Intra-Amniotic Thyroxine (T4) Absorption by the Premature Human Foetus

“…This suggests that T4 is absorbed by the human premature foetus. We have previously shown absorption of intraamniotic T4 by the ovine foetus (Sack et al 1975) and the human full-term newborn (Hobel et al 1977). The lack of change in the mean maternal serum T4 after the intra-amniotic injection suggests insignificant transfer of T4 from the foetus to the mother, or from the amniotic fluid to the mother.…”

“…This absorption is completed within 24 h. The absorbed thyroxine (T4) is distributed throughout the body as if it had been injected iv (Sack et al 1975 We also reported that the human foetus at term absorbs T4 which is ad¬ ministered intra-amniotically 12 to 24 h prior to delivery (Hobel et al 1977). We now report on our experience with T4 administered intra-amniotically into the human premature foetus.…”

Amniotic and allantoic fluid concentrations of thyroxine, 3,3′,5′-tri-iodothyronine, 3,3′-di-iodothyronine and 3′,5′-di-iodothyronine in the pig during the period of gestation

“…The mean TBG concentration in AF is 20-30 times lower than in maternal and cord serum, although the T4/TBG molar ratios are similar in both biological fluids (Sack & Fisher 1975). In the pig (Fig.…”

“…In human amniotic fluid (AF), the level of immuno¬ reactive thyroxine (T4) is very low and that of tri¬ iodothyronine (T3) is at the lower limit of detectability (Sack et al 1975). In contrast to this, 3,3',5'-triiodothyronine (reverse T3; rT3) is much higher than in maternal serum, but lower than in newborn cord serum (Klein et al 1980).…”

A Rare Case of Dyshormonogenetic Fetal Goiter Responding to Intra-Amniotic Thyroxine Injections

“…In an experimental study of pregnant sheep given intra-amniotic injections of radiolabeled T 3 and T 4 , about 90% of the injected hormones were taken up by the ovine fetus within 1 day [14]. There are no turnover studies of intra-amniotic thyroxine injected in humans, but in a study of 18 pregnant women with preeclamptic toxemia, where single doses of 500 µg of thyroxine were injected into the amniotic fluid to accelerate fetal pulmonary maturity, the amniotic total T 4 values increased more than 20-fold at 48 h, from 1.05 to 24.0 µg/dl (12.9-309 nmol/l, reference range 1.8-2.9 µg/dl) [12].…”