The effects of forskolin, cAMP, and cyanoketone on steroid-induced meiotic maturation of yellow perch (Perca flavescens) oocytes in vitro.

Intact yellow perch (Perca flavescens) follicles stimulated by 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha, 20 beta-PG) to undergo germinal vesicle breakdown (GVBD) in vitro were incubated with several agents which have been shown to increase cellular cAMP levels. Two phosphodiesterase inhibitors, SQ20,006 and isobutyl-methyl-xanthine, blocked GVBD at 1.0 mM. At lower levels (0.5, 0.1 mM) there was a dose-response effect and SQ20,006 was more inhibitory. Forskolin at 1.0-20.0 microM blocked steroid-induced GVBD, but levels of 0.1 microM or less were noninhibitory. In time-course experiments, significant inhibition of GVBD was observed when SQ20,006 (1.0 mM) was added within 6 hr after steroid stimulation or forskolin (10.0 microM) was added within 12 hr. When SQ20,006 was administered in 6-hr pulses and then removed, inhibition was observed only when the steroid was given as a 1-hr prepulse which was removed at the start of the incubation period. In this case, GVBD was blocked if the SQ20,006 pulse was given before 18 hr. At 10.0 mM, cAMP completely inhibited GVBD but was noninhibitory at lower levels. However, lower levels of cAMP (1.0, 0.5 mM) and forskolin (0.1 microM) were inhibitory if the follicles were also incubated with 1.0 microgram/ml of cyanoketone, an inhibitor of steroidogenesis. These results indicate that in vitro, increases in cAMP are inhibitory to steroid-induced meiotic maturation but may stimulate steroidogenesis in the follicle wall as well. Furthermore, in vitro steroid-stimulated maturation can be inhibited by increased cAMP for a relatively long time, following steroid treatment.