EFFECTS OF NORETHISTERONE (17α-ETHYNYL-19-NORTESTOSTERONE) AND CERTAIN OTHER STEROIDS ON THE FEMALE GONADS OF HYPOPHYSECTOMIZED IMMATURE RATS

Abstract

Several steroids, norethisterone, norethynodrel, estradiol, progesterone, testosterone propionate and 2α-hydroxymethylene-17α-methyl-dihydrotestosterone were injected subcutaneously once daily for 12 days into hypophysectomized immature female rats to demonstrate their direct effects on the gonadal morphology. The effects of 2 19-norsteroids, norethisterone and norethynodrel, are either quantitatively or qualitatively different from each other and from those of the naturally occurring sexagens such as estradiol, progesterone and testosterone.
The characteristic changes produced by norethisterone are the fluid retention under ovarian capsule, the appearance of many primary follicles in the ovaries and the typical secretory changes in uterine endometrium with glandular proliferation. However, norethisterone does not alter the reactivity of ovaries to gonadotrophins which increase the ovarian weights and produce superovulation in hypophysectomized immature female rats.
It is, therefore, difficult to support the assumption that norethisterone, one of the ovulation inhibiting agents, might have a property to depress the ovarian function, degenerate the ovarian follicles or decrease the ovarian reactivity to gonadotrophins and thus act as an anti-fertility agent. It is, therefore, concluded that the ovulation-inhibiting or anti-fertility effect of norethisterone is most likely due to the inhibition of pituitary gonadotrophin secretion.