Müllerian Inhibiting Substance As Oocyte Meiosis Inhibitor

Müllerian inhibiting substance (MIS) inhibited the resumption of meiosis in both denuded and cumulus cell-enclosed rat oocytes in vitro. Spontaneous germinal vesicle breakdown was prevented in both types of oocytes treated by a purified MIS preparation at protein concentrations of 15 micrograms to 150 pg/ml. The inhibiting effect of MIS on the resumption of meiosis was dose dependent, reversible and cyclic AMP independent. Neither follicular-stimulating hormone, luteinizing hormone, progesterone, estradiol, nor testosterone acted significantly to influence MIS-mediated inhibition of rat oocyte maturation. In contrast, MIS had no influence on meiosis in the mouse, where other protein has been reported to inhibit the cumulus cell-enclosed oocyte in a cyclic AMP-dependent fashion. Thus MIS may be yet another inhibitor of oocyte meiosis, acting in the rat by a mechanism different from those inhibitors known, in the mouse ovary, to exert their effect in a cyclic AMP-dependent manner.