Study of proliferative processes and nuclear estradiol and progesterone receptors in myocytes in pregnant and postpartum mouse uterus.

Numerical densities of the nuclei were morhometrically evaluated in all myocytes and myocytes expressing nuclear estrogen- and progesterone-receptor complexes, which were revealed immunohistochemically with monoclonal antibodies in C57Bl/6 mice. It was shown that the above quantitative parameters of myometrial cells after the first pregnancy were similar to those in nonpregnant mice by day 10 after delivery. In the third pregnancy, especially developed after the second interrupted pregnancy, proliferation processes in the myometrium were not completed by postpartum day 10, but dramatically progressed. It was associated with a significant decrease in the fraction of myocytes carrying nuclear hormone-receptor complexes with estradiol and progesterone and their disturbed physiological relations in the myometrium during and after pregnancy probably due to dedifferentiation of a considerable part of myocytes.