New methods for the regulation of implantation

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.

Synthesis of potential antiprogestins II

Alkylated derivatives of 17-acetoxyprogesterone were prepared in order to test the hypothesis that bulky groups in certain positions of the steroid molecule have the effect of transforming progestogens into antiprogestogens. These groups might exert binding influence outside the area occupied by progesterone itself. The compounds were tested for competitive affinity against tritiated progesterone and receptor from rabbit uterus cytosol. The low affinity of all derivatives makes it unlikely that they would be active as antiprogestational agents.