Receptor binding of 6 alpha-methylprogesterone in mouse kidney.

6 alpha-Methylprogesterone (6MP) is an androgenic progestin that binds to the androgen receptor. However, results from an in vivo study suggested that 6MP was also bound by a second receptor. In the present study, we found that 6MP was bound in kidney cytosol from adrenalectomized/ovariectomized female mice as well as Tfm/Y mice, which lack androgen receptors. 6MP was bound with high affinity (Kd = 1.2 X 10(-8) M) by a binder that was present in 7-8 times greater concentration than the androgen receptor and had the specificity of a glucocorticoid receptor. 6MP was bound with similar specificity in liver cytosol. These data indicate that, despite its androgenic effects, 6MP binds primarily to a glucocorticoid receptor in mouse kidney.