Characterization of the nuclear progesterone receptor in normal Premarin-primed post-menopausal endometrium

Nuclear progesterone receptors (RP_N) were characterised in a 0.4 M KC1 nuclear extract of Premarin-primed normal post-menopausal human endometrium after progesterone injection using [³H]R5020 as a ligand. The receptor character of the binding was demonstrated by the following findings: (1) the high specificity for progesterone binding; (2) the high saturable affinity (dissociation constant approx. 2.5 nM) for R5020; (3) the sedimentation coefficient at high salt concentration (approx. 3 S); and (4) the change in distribution of the RP following progesterone administration. These results indicate that normal post-menopausal human endometrium retains the property of translocation (2-step model) or nuclear activation and retention (nuclear receptor model) of the RP if it is exposed to the appropriate oestrogenic and progestational hormonal milieu.