Lack of clinical contraceptive efficacy of large doses of r 2323 given before implantation or after a missed period

The hormonal control of implantation

The hormonal control of implantation in mammalian species with and without embryonic diapause is described. In a majority of species displaying the obligate form of diapause the corpora lutea appear to exhibit a low level of steroidogenic activity throughout diapause, full luteal activity being resumed just before the initiation of implantation. Fluctuations in the plasma levels of oestrogen and progesterone during diapause may serve to prime the uterus for implantation. In species exhibiting the facultative form of diapause, such as the rat and mouse, both progesterone and nidatory oestrogen are required for the induction of implantation. In species not displaying embryonic diapause implantation will take place in the presence of progesterone alone. In the light of these considerations the selection of animal models for drug-screening purposes and possible new approaches to contraception are discussed.

Prostaglandins and progesterone receptor antagonists in human fertility regulation

Anti-progesterone medicines have now been extensively studied for human fertility regulation. The combination of the anti-progesterone Mifepristone with prostaglandin analogues such as Gemeprost and Misoprostol have been used in several European centres for medical abortion. Used before nine weeks gestation, these medicines have similar efficacy to surgical abortion. In addition, administration of progesterone antagonists within five days of unprotected intercourse appear effective in pregnancy prevention. Anti-progesterone medicines are not currently available in Australia. The introduction of progesterone receptor antagonists and modern prostaglandins would save approximately $10,000,000 per year to the Australian Health Budget. Furthermore, the introduction of progesterone receptor antagonists for emergency contraception would have even greater financial and emotional savings for Australian women. In Australia, when known carcinogens can be purchased over the counter, it is surely time for Australians to consider effective emergency contraception bought over the counter.

Mifepristone (RU486) alone or in combination with a prostaglandin analogue for termination of early pregnancy: a review

The availability of a medical mode of termination of early pregnancy by the administration of RU486, an antiprogesterone alone, or in combination with one of the PG analogues significantly reduces the maternal morbidity and mortality associated with the classical surgical abortion. RU486 given alone in early pregnancy induces complete abortion in 60% to 85% of cases, and when combined with prostaglandin analogues, gemeprost or sulprostone, reaches a success rate of 95% to 99%. RU486 may also be of potential value in the medical treatment of ectopic pregnancy. Its use as a postcoital contraception is suggested, but further research is required to determine whether RU486 can be used on a once-a-month basis for contraception.

Anti-progesterones: background and clinical physiology

The development of anti-progesterones has provided a probe to examine the role of progesterone both in the normal cycle and in pregnancy. The most widely used of these agents, mifepristone, appears to act both directly at the endometrial progesterone receptor, and centrally by reducing circulating gonadotrophin concentrations. In addition, ovarian steroidogenesis may be modified. The clinical application of these agents for the interruption of pregnancy will be considered in the following chapters.

Induction of menstruation by an antiprogesterone steroid (RU 486) in primates: site of action, dose-response relationships, and hormonal effects

The antiprogesterone compound RU 486 (17 beta-hydroxy-11 beta-[4-dimethylaminophenyl]-17 alpha-[ 1-propynyl]estra-4,9-dien-3-one; Roussel-Uclaf, Paris, France) was used to induce menstruation in a randomized controlled trial. Castrated adult female cynomolgus monkeys (n = 17) received sequential subcutaneous Silastic capsules of estradiol or progesterone over a 49-day regimen which stimulated the steroidal milieu of the fertile ovarian/menstrual cycle. RU 486 was injected at 10.0, 1.0 to 3.0, or 0.1 mg/kg from days 31 to 34 of this protocol. At all concentrations tested, menstruation followed RU 486 injection within 48 hours and persisted through 72 hours. No bleeding followed placebo injections. All monkeys that menstruated after RU 486 administration also manifested vaginal bleeding after removal of exogenous steroid treatments. No changes in daily serum follicle-stimulating hormone, luteinizing hormone, prolactin, or serum and urinary free cortisol accompanied RU 486 treatment. We conclude that (1) RU 486 promptly induces menstruation by a local action upon the endometrium; (2) familiar endometrial proliferation and withdrawal bleeding can redevelop after exposure to this compound; (3) no effects of RU 486 on serum cortisol or pituitary gonadotropins were noted; and (4) extensive combination therapy with estrogen and progesterone causes mild hyperprolactinemia.

Competitive progesterone antagonists: receptor binding and biologic activity of testosterone and 19-nortestosterone derivatives

Testosterone and 19-nortestosterone derivatives were evaluated in a developmental scheme designed to identify competitive progesterone antagonists having abortifacient activity. Compounds that displayed significant binding to the rabbit uterine progesterone receptor were followed in biologic tests for progestational, antiprogestational, and abortifacient activities. Of the seven compounds tested for both progestational and antiprogestational activity, only one, 5 alpha-dihydronorethindrone, behaved exclusively as an antagonist. Five other 19-nortestosterones (19-nortestosterone, 17 beta-hydroxyestra-4, 9(10)-dien-3-one, norethindrone, norethindrone acetate, and R 2323) proved to be mixed agonists/antagonists. 5 alpha-Dihydronorethindrone, norethindrone, and 19-nortestosterone terminated pregnancy during the postnidatory period in rats; in addition, the latter two compounds inhibited progesterone-supported pregnancy in spayed rats and curtailed pregnancy during the postnidatory period in hamsters. These results demonstrate that several 19-nortestosterone derivatives bind to the uterine progesterone receptor and behave either as antagonists or mixed agonists/antagonists.