Effects of conjugated estrogens on ripening of uterine cervix in nonpregnant castrated and pregnant rats.

The stimulating effects of conjugated estrogens (CE, Premarin) on ripening of the uterine cervix were investigated by measuring the wet weight of the cervices, as well as by both light and electron microscopic examinations on non-pregnant castrated (hereinafter called castrated) and pregnant rats. Increase in the wet weight of the cervix was observed, in comparison with lactose control group, 4 and 2 hours after administration of CE in castrated and late pregnant rats, respectively. The maximum increase in the wet weight of the cervix was evident during the period of 4 to 10 hours after administration of CE. Scanning electron microscopic investigation was carried out on the cervices using the previously defined "ripening score". The scores of castrated rats cervices taken 4 hours after administration of different amounts of CE were 24.8 +/- 1.0 (n=5, 100 microgram CE/rat) and 24.8 +/- 2.0 (n=5, 100 microgram CE/rat), showing marked increases in score, as compared with those of control. The light and transmission electron microscopic figures of the cervices of castrated rats treated with CE resembled strikingly to those of pregnant rats, and the resemblance was also striking as compared with those of castrated rats treated with free estrogens. The onset of the action of CE on the cervical capillaries was apparently faster than that on cell components of the connective tissue. There was no essential difference in ultrastructure between the cervices of lactose treated pregnant rats and CE treated pregnant ones. CE exhibited more prompt effects in increasing the wet weight of the cervix than did free estrogens in castrated rats (as observed in earlier experiments). Judging from the close resemblance between the electron microscopic figures of the CE group and those of the free estrogens group, it is postulated that the effect of CE might be due mainly to the action of free type estrogens converted from CE, and additionally, due to some unknown factors involved in the drug.