Synthetic progestins: in vitro potency on human endometrium and specific binding to cytosol receptor

The relative potency of six commonly used synthetic progestins has been evaluated in an organ culture system for human endometrium. The affinities of these progestins for endometrial progesterone receptor were also evaluated after removing the CBG-like protein by spheroidal hydroxylapatite chromatography. All six progestins induced an increase in tissue glycogen during culture at lower concentrations than did progesterone; only one (medroxyprogesterone acetate) had a relative affinity greater than progesterone. The relative potencies and affinities of the synthetic progestins were found to have the same relative order but to differ in relative magnitude.