ABSTRACT
This study investigated the interactive effects of cyanoketone (CK), an inhibitor of 3β-hydroxysteroid dehydrogenase on the effects of cAMP and forskolin (FK) on oocyte maturation in Clarias batrachus using an in vitro incubation technique. When the oocytes were incubated in the presence of 1 μg/ml 17α, 20β-dihydroxy-4-pregnen-3-one[l7α, 20β-DP, the maturation-inducing steroid (MIS) of this species] for 6h, they matured [85·3 + 1·36% germinal vesicle breakdown (GVBD)] normally after additional incubation for 20-30 h in plain medium. On the other hand, exposure to 1·0 and 8 0 mM of cAMP after MIS stimulation caused significant inhibition of GVBD but lower concentrations (0·1 and 0·5 mM) of cAMP were noninhibitory. However, when the oocytes were preincubated for 1 h with 1 μg/mI CK, a significant inhibition in the percentage of GVBD was recorded including the lower concentrations of c AMP. FK, an activator of adenylate cyclase, could significantly induce GVBD at all of its concentrations (0·1, 0·5, 1·0 and 10·0 μM) in a dose- and time-dependent manner. However, when the oocytes were exposed to 1 μg/ml CK for 1 h, prior to FK stimulation, a complete inhibition of GVBD occurred but when CK treatment was given after the FK stimulation, only a partial inhibition of maturation was observed. Taken together, these data indirectly suggest that FK induces catfish oocyte maturation probably by stimulating follicular production of Δ4 steroid ( 17α,20 β-DP)through an adenylate cyclase-c AMP-mediated pathway, a mechanism identical to the gonadotropin-induced oocyte maturation.
ABSTRACT
The effect of inhibitors in the oocyte maturation of Clarias batrachus, was investigated in vitro using actinomycin D and cycloheximide. Full-grown immature oocytes incubated with salmon gonadotropin (SG-G100) and 17α, 20ß-dihydroxy-4-pregnen-3-one at the concentration of 1 μg/ml induced 86·0 ± 1·2% and 91·3 ± 2·4% of germinal vesicle breakdown, respectively. When the oocytes were incubated with SG-G100 (1 μg/ml) + different concentrations of actinomycin D or cycloheximide, a significant drop in the frequency of germinal vesicle breakdown was observed. Thus, gonadotropin-induced maturation was inhibited by both transcriptional and translational inhibitors. When the oocytes were incubated with 17α, 20ß-dihydroxy-4-pregnen-3-one (1μg/ml) + different concentrations of cycloheximide, a significant inhibition of germinal vesicle breakdown was recorded. However, the maturation was not inhibited when the oocytes were incubated in the presence of 17α, 20ß-dihydroxy-4-pregnen-3-one (1 μg/ml) and different concentrations of actinomycin D. This suggests that mRNA synthesis is not obligatory for 17α, 20β- dihydroxy-4-pregnen-3-one induced oocyte maturation. Based on the time course experiment, it was observed that the inhibition of maturation in cycloheximide treated oocytes extends up to 12 h after which the effect becomes slowly subdued.