[Oestradiol receptors in foetal compartment (author's transl)]

Oestradiol concentration in the foetal plasma of guinea pig is 160-200 pg/ml (20-35 days of gestation), 200-300 pg/ml (35-45 days of gestation) and 170-450 pg/ml (45-60 days of gestation). After 3H-oestradiol administration to the foetus, this hormone circulates mainly as non-transformed 3H-oestradiol, 3H-oestrone and 3H-oestrone sulphate. 97-99% of the circulating oestradiol is found in unbound form. In vivo and in vitro studies in the foetus of guinea pig (40-55 days of gestation) show the presence of specific oestradiol receptors in the kidney, brain and Mullerian ducts of the foetus. The affinity constant in the cytosol of the brain is Kd=2 X 10(=9)M; in the cytosol kidney this value is Kd = 2.3 X 10(=10)M. A direct binding of 3H-oestradiol to the chromatin of the kidney was demonstrated with a Kd = 3.3 X 10(=10)M In the cytosol of Mullerian ducts the presence of a specific 3H-oestradiol macromolecule component with a sedimentation coefficient (in sucrose gradient) of 8-8.5S was detected. It is concluded that specific oestradiol receptors are present during foetal development in tissues such as kidney, brain and Mullerian ducts, but not in the liver.