Effects of medroxyprogesterone acetate and chlorpromazine on ovulation and vaginal cytology in a strain of 4-day cyclic rats

Abstract

A correlation observed between the vaginal cornification and the presence of freshly shed ova in the fallopian tube in a strain of 4-day cyclic rats was altered by administering medroxyprogesterone acetate (MPA) and chlorpromazine (CPZ). MPA, given 1 day before proestrus, blocked vaginal cornification, uterine fluid imbibition, and ovulation. A single injection of human chorionic gonadotropin (HCG), given on the expected day of proestrus, induced ovulation in all MPA-treated rats, but did not induce estrogenic parameters. CPZ, given at noon on the day of proestrus, also blocked ovulation, but did not alter the estrogenic effects. Again, HCG induced ovulation in CPZ-treated rats. These data indicate that MPA and CPZ have a similar pharmacologic effect at the hypothalamus–pituitary axis, while acting differently at the estrogenic receptor sites.