SAITO, Y., TAKAHASHI, S. and MAKI, M. Effects of Some Drugs on Ripening of Uterine Cervix in Nonpregnant Castrated and Pregnant Rats. Tohoku J. exp. Med., 1981, 133 (2), 205-220-The stimulating effect of some drugs on the ripening of the uterine cervix in rats was studied by measuring the wet weight of the uterine cervix and by both light and electron microscopy in nonpregnant castrated and pregnant conditions. Since the light and electron microscopic findings after estrogen (E) administration to castrated rats were similar to those found in the uterine cervix of rats at the end of pregnancy, it was concluded that E (E₂≥E₃>E₁) plays a major role in the ripening mechanism. It was also found that DHA-S, progesterone and relaxin had stimulating effects on cervical ripening. Oxytocin and PG (PGE₂>PGF_2α) showed the ripening activity only in pregnant condition. Moreover, oxytocin, PGE₂ and PGF_2α potentiated the estrogen action. The effects on the increase in wet weight of the uterine cervix and microscopic findings due to DHA-S were different from E in castrated rats. It is therefore postulated that the effect of DHA-S might be mainly due to the secondary increase in E converted from DHA-S in the ovary and, in addition, to a direct effect of this medicament on the uterine cervix. There was essentially no difference in ultrastructure between the cervix of control (nonpregnant, castrated or pregnant) rats and that of rats treated with HCG, isoxsuprine hydrochloride, dihydroergotoxine, diazepam or n-butylscopolammonium bromide.