Relative in vitro effectiveness of 17α,20β-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 autatus)

Abstract

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, 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-diOHprog) was consistently the most potent inducer of final oocyte maturation. Both progesterone and 17α-hydroxyprogesterone were effective at relatively high concentrations. Of the 5β-reduced metabolites, 17α,20β-dihydroxy-5β-pregnan-3-one was almost as effective as 17α,20β-diOHprog in oocytes of amago salmon and rainbow trout, while the other 5β-reduced compounds (3α-hydroxy-5β-pregnan-20-one, 17α-hydroxy-5β-pregnane-3,20-dione, 3α,17α-dihydroxy-5β-pregnan-20-one, 5β-pregnane-3α,17α,20β-triol, and 5β-pregnane-3β,17α,20β-triol) were almost or totally ineffective at the concentrations tested (1–0.001 μg/ml). These bioassay results, together with previous findings on the capacity of the ovary to produce 17α,20β-diOHprog, indicate that 17α,20β-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 17α,20β-diOHprog is involved in maturation of goldfish oocytes, since supportive physiological and biochemical data are lacking. Possible regulatory roles of 5β-reduced metabolites on steroid-induced oocyte maturation are discussed.