Evidence for the stimulation of cyclic AMP phosphodiesterase in catfish (Clarias batrachus) oocytes by 17α,20β-dihydroxy-4-pregnen-3-one

Abstract

A decrease in cyclic AMP (cAMP) level within the catfish follicle occurs during oocyte maturation (Haider and Chaube [1995] Comp. Biochem. Physiol., 112A:379-385). Experiments described in this report were performed to evaluate the modulations in oocyte phosphodiesterase (PDE) activity during maturation in the catfish Clarias batrachus. An increase in PDE activity was found in extracts of oocytes which were incubated for 36 hr with different concentrations of 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DP; the naturally occurring maturation-inducing steroid of this catfish), and this increase was in a dose-dependent manner. Evaluation of the time course of response to 1 μg/ml 17α,20β-DP revealed that PDE activity increased in a time-dependent manner. A minimum detectable PDE activity was observed at 2 hr, the half-maximal activity at 6 hr, and maximum at 36 hr of incubation of oocytes with 17α,20β-DP. The two different known inhibitors (isobutylmethylxanthine and theophylline) inhibited catfish oocyte PDE activity in a dose-dependent manner. These studies suggest that the 17α,20β-DP-induced increase in PDE is involved in the decrease in cAMP in catfish oocytes during maturation.