LEVELS OF L-T3 IN MATERNAL AND FETAL COMPARTMENTS FOLLOWING EXPERIMENTAL MODIFICATIONS OF THE MATERNAL THYROID STATE IN RATS

In pregnant female rats, concentrations of tri-iodo-L-thyronine in mat ernal serum, amniotic fluid and placental tissue after 15, 18 and 20 d ays of gestation were measured by homologous radioimmune-analysis. The three experimental groups of pregnant rats were : 1) euthyroid (or co ntrol), 2) hypothyroid, provoked by iodine-deficient diet for two mont hs before conception and during gestation, 3) hyperthyroid, provoked b y subcutaneous injections of L-thyroxine during gestation. Maternal se rum L-T3 was measured in order to check the thyroid state. Significant decreases in L-T3 concentrations were found at all stages of gestatio n in the amniotic fluid of hypothyroid group. The hormonal concentrati ons in the placental tissues were correlated with the different treatm ents (decreased in hypothyroid state and increased in hyperthyroid sta te). This could suggest that the transfer of maternal iodothyroinines to the foetus influences its foetal thyroid development.