[Anti-implantation effect and morphological changes of corpus luteum and endometrium in rat by estriol]

The anti-implantation effect of estriol on rats was studied by enzyme histochemical methods. The activities of 3beta-hydroxy-steroid dehydrogenase (3beta-HSD), AcP in corpus luteum, A1P in endometrium of treatment groups were compared with those of control groups. In order to know the effect of estriol on endometrium during preparing for blastocyst implanting, we counted the number of mitosis cell in endometrium of 4th day pregnant rat under microscope. Serum progesterone level of early pregnant rats was measured by radioimmunoassay the results were as follows: 1. Estriol administrated postcoitally could prevent the early pregnancy of rats by the way of anti-implantation of blastocyst; 2. Activity of ovarian corpus luteal 3beta-HSD was depressed, whereas activity of AcP increased in the treatment group; 3. The number of mitotic cell in endometrial stroma was: in the treatment group 0.2 +/- 0.2, in the control group 45.7 +/- 16.2 (P less than 0.001); A1P reaction of endometrial stroma was negative in the treatment group, whereas it was positive in the control group; and 4. The serum progesterone level was: in the treatment group 17.4 +/- 12.6, in the control group 39.3 +/- 11.1 ng/ml (P less than 0.01). The results suggest that estriol can disturb the biosynthesis of progesterone of corpus luteum and reduce the serum progesterone level. Mitosis and decidulization of stroma cell can be disturbed owing to the low serum progesterone level, so the blastocyst cannot be implanted successfully.