Is Provera the ideal progestogen for addition to postmenopausal estrogen therapy?

In a dose-ranging study, medroxyprogesterone acetate, 2.5, 5, or 10 mg daily, was given for 12 days of each calendar month to postmenopausal women also receiving conjugated estrogens, 0.625 mg daily, continuously. Endometrial biopsy specimens were taken on the sixth day of combined therapy for histologic, ultrastructural and biochemical evaluation. Medroxyprogesterone acetate induced secretory and ultrastructural changes within the endometrium, but the responses were variable and inconsistent. Suppression of epithelial deoxyribonucleic acid synthesis appeared dose-dependent. The levels of nuclear estradiol receptor, although reduced to within the secretory phase range, were not significantly lower than the values observed during the estrogen-only phase of treatment. Induction of both estradiol and isocitrate dehydrogenase activities was to within the secretory phase ranges, but the magnitude of these responses appeared less than those observed previously with other progestogens. Both morphologically and biochemically, medroxyprogesterone acetate, even at high dosage, produced suboptimal responses. Further studies are required to establish whether this is a dose-related effect.