Relative in vitro effectiveness of 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one and other pregnene derivatives on germinal vesicle breakdown in oocytes of ayu (Plecoglossus altivelis), amago salmon (Oncorhynchus rhodurus), rainbow trout (Salmo gairdneri), and goldfish (Carassius auratus).

The relative effectiveness of several pregnene derivatives, which had previously been identified in the ovaries of ayu (Plecoglossus altivelis), on germinal vesicle breakdown (GVBD) was investigated in vitro using folliculated oocytes of four species of teleosts, ayu, amago salmon (Oncorhynchus rhodurus), rainbow trout (Salmo gairdneri), and goldfish (Carassius auratus). Although some species differences existed in the relative effectiveness of each steroid on GVBD, 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha, 20 beta-diOHprog) was consistently the most potent inducer of final oocyte maturation. Both progesterone and 17 alpha-hydroxyprogesterone were effective at relatively high concentrations. Of the 5 beta-reduced metabolites, 17 alpha, 20 beta-dihydroxy-5 beta-pregnan-3-one was almost as effective as 17 alpha, 20 beta-diOHprog in oocytes of amago salmon and rainbow trout, while the other 5 beta-reduced compounds (3 alpha-hydroxy-5 beta-pregnan-20-one, 17 alpha-hydroxy-5 beta-pregnane-3,20-dione, 3 alpha, 17 alpha-dihydroxy-5 beta-pregnan-20-one, 5 beta-pregnane-3 alpha, 17 alpha, 20 beta-triol, and 5 beta-pregnane-3 beta, 17 alpha, 20 beta-triol) were almost or totally ineffective at the concentrations tested (1-0.001 micrograms/ml). These bioassay results, together with previous findings on the capacity of the ovary to produce 17 alpha, 20 beta-diOHprog, indicate that 17 alpha, 20 beta-diOHprog is the natural maturation-inducing steroid hormone common to three species of Salmoniformes, ayu, amago salmon, and rainbow trout. These results, however, only suggest that 17 alpha, 20 beta-diOHprog is involved in maturation of goldfish oocytes, since supportive physiological and biochemical data are lacking. Possible regulatory roles of 5 beta-reduced metabolites on steroid-induced oocyte maturation are discussed.