Two new types of antiprogestins that can suppress menstruation and could end the monthly misery many women suffer have passed their first tests in animals, scientists report in Europe's leading reproductive medicine journal, Human Reproduction.*
Studies in rhesus macaque monkeys show that that one drug - ZK 137 316 - can, depending on dose, allow ovulation but block menstruation, while the other - ZK 230 211 - blocks both ovulation and menstruation. Of great importance, both the drugs block the effects of oestrogen on the lining of the uterus, thus preventing the potentially dangerous build-up of endometrial cells caused by the action of unopposed oestrogen.
The studies have been carried out in Dr Robert Brenner's laboratory in the Division of Reproductive Sciences at Oregon Regional Primate Research Centre in the USA.
Rhesus macaque monkeys were used because they are one of the only animals that regularly menstruates and the mechanism in the brain, ovary and uterus controlling their periods is identical to that of humans. According to Dr Brenner, senior scientist with the Oregon Center, the results should therefore be directly applicable to women.
He said: "A reliable means of menstrual suppression would greatly improve the quality of life for women. The modern woman is accustomed to having control over her reproductive functions and menstruation is one function that many women would like to control. It is possible to use the oral contraceptive pill without the pill-free interval for this purpose, but not all women can tolerate the Pill and there are some health conditions that proscribe its use.
"Our goal in these studies was to obtain pre-clinical data prior to clinical development, and these results are very encouraging. All the treated animals, regardless of the dose they were given, remained in good health, maintained normal follicular phase concentrations of oestradiol and returned to normal menstrual cycles within 15 to 41 days after treatment stopped."
He said that his laboratory was now working on some of the cellular mechanism underlying the actions of the compounds and collaborating on the next generation of progesterone receptor antagonists with menstruation suppression potential. These compounds have potential tested for suppressing medical conditions such as endometriosis** and uterine fibroids.
Said Dr Brenner: "These new menstrual suppressants are novel in that they use very low doses of progestin antagonists administered for as long as a woman desires to suppress menstruation, and that once the treatment is stopped normal cycles begin again in a very short time. The fact that we have an animal model with a cycle identical to that of a woman has been extremely valuable as it has enabled us quite quickly to develop these potential treatments to the point where they should be available to women within a few years. I would emphasise that we are not talking here only about lifestyle choices but also about the potential to bring relief to the many women who suffer years of misery from distressing complaints such as endometriosis, and painful and excessive monthly bleeding. In fact, excessive bleeding is one of the major reasons that women undergo hysterectomy***, and this treatment may also reduce the need for this surgical procedure, with all its attendant risks and costs."
* Reversible suppression of menstruation with progesterone antagonists in rhesus macaques. Human Reproduction. Vol 16. No 8. pp 1562-1574.
** Endometriosis: a difficult-to-treat condition in which clumps of cells that line the uterus escape from the womb and become deposited on other organs in the pelvis, bleeding at the time of periods and causing pain and even infertility in severe cases.
*** Hysterectomy: surgical removal of the uterus
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