On the effects of cyanoketone on gonadotrophin- and steroid-induced in vitro maturation of Oryzias oocytes.

Effects of cyanoketone (CK) on the gonadotrophin- and steroid-induced maturation in vitro of Oryzias latipes oocytes were examined. In oocyte covered with intact follicle or granulosa cell layers, CK inhibited gonadotrophin- and pregnenolone-induced maturation but not 20 beta-OH-progesterone-induced maturation. However, when follicle cells were removed completely from the oocytes, CK conspicuously lacked inhibitory effect on pregnenolone-induced oocyte maturation. It was ascertained by using purified pregnenolone that pregnenolone-induced maturation was not due to contamination with other maturation-inducing steroids. It was also observed immunocytochemically that a purified pregnenolone stimulated in vitro production of progestins in the granulosa cells, and that CK inhibited this stimulation. These results indicate that pregnenolone, like gonadotrophin, induces maturation of intrafollicular oocytes of O. latipes by stimulation of production of such steroids as progesterone in follicle cells (granulosa cells), while it can directly induce maturation of oocytes not surrounded by follicle cells.