gonadotropin-induced steroidogenic shift
towards maturation-inducing hormone in Japanese yellowtail during final
oocyte maturation
M. A. Rahman, K. Ohta, H. Chuda, S. Nakano, K.
Maruyama, M. Matsuyama-2001
Journal
of Fish Biology, 58(2): 462-474
Abstract:
Intact
ovarian follicles, obtained from untreated and human chorionic
gonadotropin (HCG) treated Japanese yellowtail Seriola
quinqueradiata during different maturational
stages, were incubated with radioactive [3H]pregnenolone,
[3H]17-hydroxyprogesterone or [14C] androstenedione
and steroid metabolites identified by thin layer
chromatography (TLC) followed by recrystallization to
constant specific activity. In untreated late
vitellogenic (0h) follicles, androstenedione was the major product with smaller amounts of testosterone and
oestradiol-17β. In post-vitellogenic (12h
post-injection) intact follicles, androstenedione
predominated, and although testosterone and oestradiol-17β
were not produced, there were small amounts of 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and 17,21-dihydroxy-4-pregnene-3,20-dione (11-deoxycortisol). In HCG-treated fish, a steroidogenic shift resulted in the disappearance of testosterone and oestradiol-17β coinciding with the appearance of 17,20β-P.
During early and late final oocyte maturation FOM (24 and 36h post-injection), there was a five- to seven-fold increase in the production of 17,20β-P, whereas production of 11-deoxycortisol remained almost the same. During FOM, in addition to 17,20β-P, its 5β-reduced metabolite, 17,20β-dihydroxy-5β-pregnan-3-one (5β-17,20β-P) was synthesized, suggesting a decrease in maturation-inducing 17,20β-P activity. 17,20β,21-Trihydroxy-4-pregnen-3-one (20β-S) was not synthesized by ovarian fragments in Japanese yellowtail at any maturational stage. The metabolites identified on TLC during FOM were tested to
evaluate their maturation-inducing activity in an in vitro bioassay. Of the steroids tested, 17,20β-P was the
most effective inducer of germinal vesicle breakdown
(GVBD), followed by 5β-17,20β-P. Timely synthesis of
17,20β-P immediately prior to and during FOM as
well as its great potency in inducing GVBD in vitro supports
the evidence for a physiological role of 17,20β-P
as a maturation-inducing hormone in Japanese yellowtail.
(Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu
University, Fukuoka, 812-8581, Japan, Tel.: +81 92 642 2887;
Fax: +81 92 642 2888; E-mail of M. Matsuyama: