Attachment reaction of rat uterine luminal epithelium V. Suppression of the attachment reaction by some antifertility agents

The effects of the postcoitally active antifertility agents U-11,555A, U-11,100A, MER-25, ICI-46,474, 66/179, F-6103, F-6255, F-6278 and ORF-4563 on the ultrastructure of the rat uterine luminal epithelium were studied in spayed, virgin rats under three experimental conditions.

1. Expt. I. When given separately, all agents gave an estrogen-like response. This was most marked with the F-compounds and ORF-4563.

2. Expt. II. In progesterone-treated rats, the F-compounds and ORF-4563 changed the ultrastructure profoundly, while the other compounds had little effect.

3. Expt.III. A combination of progesterone and estradiol renders the epithelium suitable for implantation; a parallel change in the ultrastructure is the attachment reaction.

When given before estradiol, each compound except U-11,555A inhibited the attachment reaction in most animals.

In conclusion, the F-compounds and ORF-4563 had strong estrogenic effects in all tests. Their antifertility activity is probably related to this property. The other substances were almost indistinguishable from estradiol in Expt. I but did not induce an attachment reaction in Expt. II as estradiol does. In Expt. III these substances, except U-11,555A, seemed to act like anti-estrogens, interfering with the attachment-inducing effect of estradiol, which may explain their antifertility activity. How U-11,555A exerts its antifertility activity is not clear.