Steroid enhancement of Mullerian duct regression

The biologic activity of the glycoprotein, Mullerian Inhibiting Substance (MIS), was enhanced by added testosterone, medroxyprogesterone acetate, and progesterone, although these steroids did not cause Mullerian duct regression when added alone. Statistically significant augmentation by testosterone and medroxyprogesterone was observed at concentrations of 10(-7) and 10(-8) M. Progesterone enhanced MIS activity at a concentration of 10(-6) M. By contrast, dihydrotestosterone, estradiol, and corticosterone at concentrations of 10(-9) to 10(-5) M produced no significant effect on MIS activity. Since MIS does not bind directly to the steroids studied, we suspect that the enhancement effect occurs at the receptor level, probably at the mesenchyme as observed in other developmental systems.