Biochemical and histologic effects of sequential estrogen/progestin therapy on the endometrium of postmenopausal women.

Medroxyprogesterone acetate in doses of 10, 5, and 2.5 mg was administered sequentially to three groups of postmenopausal women receiving 0.3 mg, 0.625 mg, and 1.25 mg of conjugated equine estrogens, respectively. Serial endometrial biopsies were performed on these women before therapy, during estrogen therapy alone, and during sequential estrogen-progestin therapy. Endometrial histology and estrogen receptor concentrations were assessed. A linear increase of cytosolic estrogen receptor concentration occurred over the dosage range of conjugated equine estrogen. When medroxyprogesterone acetate was added to the estrogen therapy, the concentrations of estrogen receptors fell. Within the groups of women receiving 0.3 mg and 0.625 mg of conjugated equine estrogen, all doses of medroxyprogesterone acetate were equally effective in reducing the levels of cytosolic receptor to pretreatment levels. However, at the conjugated equine estrogen dose of 1.25 mg, only 5 mg and 10 mg doses were effective in reducing the cytosolic receptor concentration to pretreatment levels. Histologically, little effect was observed from the lowest doses of either drug. However, even though 5 and 10 mg of medroxyprogesterone acetate were identical biochemically, the 10 mg dose was the only one producing a homogeneous, secretory pattern within the endometrium.