Ovarian metabolic pathways of steroid biosynthesis in the European eel (Anguilla anguilla L.) at the silver stage

Abstract Ovarian slices of the European eel at the silver stage were incubated with 4 tritiated precursors (pregnenolone, progesterone, androstenedione, testosterone) in the presence or not of an inhibitor of 11β-hydroxylase activity, metopirone. Ether extracts were submitted to a gradient elution chromatography on celite columns. Isolated peaks were identified by isopolarity on TLC, microchemical reactions and recrystallization to constant specific activity. Interpretation of the results shows that the ovary of the European eel contains the following enzymes: a 3β-hydroxysteroid dehydrogenase, 5→4-ene-isomerase complex, a 17α-hydroxylase, a C 21 -C 19 desmolase, a 17β-hydroxysteroid oxidoreductase, a 5α-reductase, a 3β-hydroxysteroid oxidoreductase and an aromatase complex. Metopirone effect indicates the presence of an 11β-hydroxylase activity. At this stage, 5β-reductase, 20β-reductase and 21-hydroxylase activities are not detected in the ovary. Water-soluble steroids were formed from all the precursors used. It appears that the ovarian biosynthesis is orientated towards the production of 5α-reduced compounds and that this might limit the production of 17β-estradiol by lowering the amount of disposable endogenous precursors.