Steroid biosynthesis by the ovary of the European eel, Anguilla anguilla L., at the silver stage.

The ovary of the European eel, Anguilla anguilla, at the silver stage, was incubated either as an intact tissue preparation or as a homogenate with and without cofactors in the presence of 4-¹⁴C] pregnenolone and 4-¹⁴C]progesterone. Intact tissue incubates displayed a more complex metabolite profile than reinforced homogenates, and deprivation of exogenous cofactors reduced the profile even further. Among the metabolites derived from pregnenolone, the following steroids were identified by their isopolarity and isomorphicity with standard compounds: 17α-hydroxypregnenolone; dehydroepiandrosterone; progesterone; 17α-hydroxyprogesterone; and androstenedione. The last three steroids plus testosterone, 17β-hydroxyandrostenedione, and adrenosterone were identified using progesterone as a precursor. Metopirone inhibited the formation of 11-oxygenated androgens. 11-Deoxycorticosteroids were not found, indicating the absence of steroid 21-hydroxylase activity in the eel ovary. Integration of the product yield-time curves demonstrates that in vitro the activities of the enzymes 3β-, 17β-, and 11β-hydroxysteroid dehydrogenases were less apparent than those of steroid 17α,20-C₂₁-desmolase, and 17α-, and to a lesser extent 11β-hydroxylase. Irrespective of the incubation conditions, pregnenolone produced more Δ⁵-3β-hydroxy-thanΔ⁴-3-ketosteroids, suggesting a predominance of the former biosynthetic pathway. Among the unidentified metabolites, water-soluble compounds were formed from both precursors in intact tissue incubates.