Shift in steroidogenesis in the ovarian follicles of the goldfish (Carassius auratus) during gonadotropin-induced oocyte maturation

Abstract

Both partially purified chum salmon gonadotropin and 17α-hydroxyprogesterone stimulated in vitro production of testosterone by postvitellogenic follicles of goldfish (Carassius auratus). Chum salmon gonadotropin further enhanced the conversion of exogenously supplied 17α-hydroxyprogesterone to 17α, 20β-dihydroxy-4-pregnen-3-one. The increased medium concentrations of 17α, 20β-dihydroxy-4-pregnen-3-one were associated with the induction of final oocyte maturation.

The capacity of postvitellogenic follicles to produce steroids in response to exogenous 17α-hydroxyprogesterone was examined in females at various stages of final oocyte maturation following the administration of human chorionic gonadotropin in vivo combined with elevation of holding temperature. The maximum production of testosterone in response to 17α-hydroxyprogesterone was obtained in follicles from initial controls. In contrast, 17α 20β-diOHprog production was very low in initial controls and markedly increased during oocyte maturation (3–6 hr following injection), followed by a significant decrease in follicles collected at 15 hr. Estradiol-17β production by the follicles was very low at any stages of gonadotropin-induced oocyte maturation. These results suggest that gonadotropin-induced shift in the biosynthetic pathway in the follicle from the secretion of predominantly testosterone to 17α, 20β-dihydroxy-4-pregnen-3-one secretion is a prerequisite step for the induction of oocyte maturation in goldfish.