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Comment |
Up-regulation of cGMP-specific phosphodiesterase in the porcine cumulus-oocyte complex affects steroidogenesis during in vitro maturation. Sasseville M et al. The 3'5'-cyclic guanosine monophosphate (cGMP) pathway is known to influence ovarian functions, including steroidogenesis, ovulation, and granulosa cell proliferation. We show here that cGMP-phosphodiesterase activity increased in a gonadotropin-dependent manner more than 3-fold in the cumulus-oocyte complex (COC) after 24 hours of in vitro maturation and up to 5-fold after 48 hours. Further characterization of this increase demonstrated that the activity was located primarily in cumulus cells and was sensitive to sildenafil and zaprinast, two inhibitors specific to both type 5 and type 6 phosphodiesterases. Reverse transcription-PCR experiments showed that the mRNAs for cGMP-degrading phosphodiesterases 5A and 6C are present in the COC before and after 30 hours of in vitro maturation. Western blotting confirmed the presence of phosphodiesterase 5A in the COC. Western blotting of phosphodiesterase 6C revealed a significant up-regulation in the COC during in vitro maturation. Isolation and analysis of detergent-resistant membranes suggested that phosphodiesterase 6C protein, along with half of the total sildenafil-sensitive cGMP-degradation activity, is associated with detergent-resistant membrane in the COC after 30 hours of in vitro maturation. Treatment of porcine COC with sildenafil during in vitro maturation caused a significant decrease in gonadotropin-stimulated progesterone secretion. Together, these results constitute the first report exploring the contribution of cGMP-phosphodiesterase activity in mammalian COC, supporting a functional clustering of the enzyme, and providing the first evidence of its role in steroidogenesis.
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