Effects of steroids on germinal vesicle breakdown in vitro of intact follicles in the japanese whiting, Sillago japonica, a marine teleost

1. 1. The effects of various steroids on germinal vesicle breakdown (GVBD) of follicle-enclosed oocytes of the Japanese whiting were examined by using an in vitro incubation technique. 2. 2. Of the stimulatory steroids, 17α,20β-dihydroxy-4-pregnen-3-one was the most effective, inducing 72% GVBD at concentrations as low as 0.1 ng/ml. The next most potent steroid was 20β-dihydroprogesterone, inducing 33% GVBD at concentrations of 0.1 ng/ml. 3. 3. The specificity for steroid-stimulated GVBD in Japanese whiting is consistent with several previous studies involving salmonids and various other teleosts, and suggests a possible physiological role for a 20β-dihydroprogestin in oocyte maturation of Japanese whiting.