CONTROL MECHANISMS OF STEROID HORMONE RECEPTORS IN THE REPRODUCTIVE TRACT

The hormonal control of the amount of steroid receptors in the target cells may be a clue for the understanding of hormone receptivity and of integrated hormonal mechanisms (for example cyclic sequences of events). As a model system, the guinea pig uterus progesterone receptor has been studied. After an analysis of the theoretical and practical parameters which should be taken into account in order to measure specifically the receptor binding sites, the protein-RNA synthesis mediated induction of the progesterone receptor by oestradiol is described. The half life of the receptor is about 5 days in hormone deprived animals (in vivo experiments), but in case of progesterone administration it decays very rapidly, due probably to a rise in inactivation rate. Sequential administration of oestradiol and progesterone reproduces the changes observed during the oestrous cycle. The mechanism of the apparent inactivation of the receptor after binding of its own hormonal ligand is unknown. Some information available about the hormonal control of the androgen and oestrogen receptors in their respective target organs is reviewed.