[Receptiveness to sexual steroids. Physiopathological aspects]

Each hormonal signal is specifically related to a cellular receptor. However, the same receptor may bind several hormones. Oestradiol which binds to the oestrogenic receptor with a Kd of 0,1 nM, may also bind with the prostatic androgen receptor with a Kd of 3 nM. Progesterone is another example of binding pluralism as it binds not only to the progesterone receptor but also to the androgenic (anti-androgenic effect), mineralocorticoid receptors (anti-aldosterone effect) and the gluco-corticoid (anti-inflammatory effect. As different receptors may bind the same steroid, reciprocally, a given receptor may bind different steroids. What applies to natural hormones, also applies to synthetic hormones. Each new molecule has a specificity of biological action which can be predicted from pharmacological screening tests. This specificity is expressed by the affinity of relative binding to a given receptor compared with a reference steroid. In vitro studies do not take endogenic metabolism which may alter the concentration of the tested substances at the receptor site into account. The modes of receptivity to steroid hormones are complex and other factors than the receptor proteins are involved. The change in uterine blood flow induced by oestradiol cannot be explained by these mechanisms. Similarly, progesterone acts at the cell membrane level of the amphibian egg. The receptivity to sexual steroids is therefore a complex phenomenon, the first elements of which are beginning to be understood.