Immunohistochemical Determination of Endometrial Progesterone Receptor (PR) Content after Intrauterine Infusion of Danazol in Rabbits

Danazol, an isoxazol derivative of 17 α-ethinyl-testosterone, has various effects on the female reproductive system. To examine its anti-estrogenic effects through the receptor system and clarify its direct effect on the endometrium in vivo, we applied danazol jelly into the rabbit uterine cavity.Recent studies performed in our laboratory using the ligand-binding assay have shown that danazol administered directly into the uterine cavity is absorbed by the endometrial tissue and exerts its anti-estrogenic effects possibly through progesterone receptors (PR) in the cells. In the present study we examined the variations in endometrial PR content during 7 days after the intrauterine administration of danazol into the rabbit uterine cavity. Immature female white rabbits were used. They were given daily subcutaneous injections of estradiol-17β (E2) for 3 days after which their abdomens were opened, and danazol gel was infused into the lumen of the right horn and HPC-jelly was infused into the lumen of the left horn, as the control. Thereafter and until they were killed, the same daily dose of E2 was injected. They were killed 6h, 24h, 3 days, 5 days or 7 days after intrauterine infusion of danazol and PRs were studied immunohistochemically using a specific antireceptor monoclonal antibody (PR-AT 4.14). Six hours after danazol infusion, the PR staining in the glandular epithelium and part of the stroma surrounding the epithelium had declined. On day 3, PR staining declined to its lowest level in the glandular epithelium and stroma. On Day 5, PR staining had been restored in the glandular epithelium but stayed low in the stroma. The PR staining had been restored completely on Day 7. On the other hand, PR staining in the myometrium remained unchanged throughout the 7 days the experiment lasted. We conclude that danazol administered into the uterine cavity is absorbed by the endometrial tissue and binds to PRs directly. The effect of danazol on the receptor level lasted for at least 7 days. Thus, it seems there is some kind of barrier at this level which prevents danazol permeation through the myometrium.