In vitro biosynthesis of oestradiol-17β and 17α,20gb-dihydroxy-4-pregnen-3-one by vitellogenic ovarian follicles from migrating New Zealand longfinned eels ( Anguilla dieffenbachii)

Abstract

In vitro oestradiol-17β (E 2) and 17α,20β-dihydroxy-4-pregnen-3-one (17,20-DHP) production by vitellogenic ovarian tissue from Anguilla dieffenbachii captured during the natural spawning migration was examined. Ovarian fragments were incubated with or without human chorionic gonadotropin (hCG) in the presence or absence of pregnenolone, androstenedione or testosterone. Despite relatively high E 2 levels in vivo (2.48 ± 0.28 ng ml −1, n = 7), in vitro e 2 production was low. In contrast, 17, 20-DHP levels were low in vivo (less than 0.16 ng ml −1), while production was high in the presence of pregnenolone in vitro, indicating strong 20β-hydroxysteroid dehydrogenase activity in vitellogenic follicles. Addition of hCG did not significantly stimulate E 2 or 17,20-DHP production above that of controls in any of the incubations. These results are in contrast to those arising from similar studies in salmonids and indicate that the models developed for control of E 2 and 17,20-DHP production by the salmonid follicle may not be fully applicable to the eel follicle.