[Gestational changes of cytoplasmic and nuclear estrogen and progesterone receptors in the human myometrium (author's transl)].

The gestational changes of both cytosol and nuclear estrogen and progesterone specific binding sites in human myometrial were studied to evaluate the role of these steroids in the mechanism of initiating labor. 1) In nonpregnant women, early and term pregnancy, the dissociation constants (Kd) of cytosol estradiol-17 beta (ERc) and progesterone (PRc) showed no change but the number of binding sites (NBS) of the former varied from 275 +/- 1.3 to 5.5 +/- 0.1 and 10.0 +/- 2.0 (x 10(-15) mol/mg protein) and the latter from 2.5 +/- 0.5 to 25.5 +/- 3.2 to 3.8 +/- 0.8, respectively. The number of nuclear acceptor sites of estradiol-17 beta (EAn) changes during this period from 4.0 +/- 1.5 to 5.0 +/- 1.0 and 0.6 +/- 0.3 (x 10(-15) mol/g DNA), while those of progesterone (PAn) are from 1.3 +/- 0.3 to 1.2 +/- 0.5 and 0.3 +/- 0.1, both showing a significant decrease towards term. 2) After the onset of labor, the nuclear acceptor sites increased significantly (RAn: 0.6 +/- 0.3/4.3 +/- 1.0, PAn: 0.3 +/- 0.1/3.3 +/- 0.8 x 10(-15) mol/micrograms DNA, p less than 0.01), while those in the cytosol remained unchanged. 3) Te ERc/PRc ratio of Kd unchanged throughout pregnancy but that of NBS increased a term (p less than 0.01) and the ratio of EAn/PAn decreased (p less than 0.05). This change became more apparent after the onset of labor. These findings suggest that at term, the myometrial hormone environment becomes dominant and this intracellular change of hormone sensitivity play an important role in the mechanism of initiating human parturition.