Medroxyprogesterone acetate binding sites in human endometrium and endometrial cancer

Medroxyprogesterone acetate (MPA) binding sites in both human normal endometrium and endometrial carcinoma were identified and characterized by sucrose gradient centrifugation. These binding components were divided into two classes by saturation analysis, one with high affinity and low capacity and the other with low affinity and high capacity. The concentrations of low-affinity binding sites for MPA in endometrial carcinoma were higher than those in normal endometrium (p less than 0.01). By sucrose gradient centrifugation, 4S and 8S components were observed in both high- and low-affinity binding sites of normal endometrium. These components were moved to 4S by the addition of salt. However, in endometrial carcinoma, low-affinity binding sites were displayed at about 4S under either low- or high-salt conditions. High-affinity binding sites in endometrial carcinoma had the same sedimentation patterns as in normal endometrium. An obvious difference between normal endometrium and endometrial cancer was observed in low-affinity binding sites. Our results on the binding sites for MPA suggest that low-affinity binding sites may be related to the response of endometrial cancer to high-dose MPA treatment.