Suppression of reproductive function in autoimmune NZB/W mice: effective doses of four contraceptive steroids.

Oral contraceptives have been implicated in causing flares of systemic lupus erythematosus in humans, and studies of these agents in the NZB/W mouse model of lupus may help to elucidate mechanisms responsible for disease activation. To define doses which effectively suppress reproductive function in NZB/W mice, we implanted groups of NZB/W females with Silastic capsules containing increasing doses of four compounds: norethindrone (NE) 0.5-5.0 mg, norgestrel (NG) 1.0-7.5 mg, medroxyprogesterone (MP) 0.5-20.0 mg, and ethinyl estradiol (EE) 0.5-5.0 mg. Controls received empty implants. Serum concentrations of LH and FSH, uterine weight, endometrial proliferation, and luteal tissue were assessed after 3 weeks of treatment. Based upon these parameters, we determined that effective doses were 5.0 mg NE, 7.5 mg NG, and 0.5 mg EE given as single implants and 10.0 mg MP given in two 5.0-mg implants. This is the first dosing study of contraceptive steroids in a murine model of lupus. Effective, nontoxic doses of these drugs can now be employed in studies of interactions between gonadal hormones and autoimmunity.