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Background: The purpose of this study was to evaluate the effect of phosphodiesterase I (PDE I) on in vitro maturation of immature NMRI mouse strain oocyte.
Materials and Methods: In this experimental study, immature oocytes recovered from NMRI mouse strain (4-6 weeks) were categorized in one control and ten experimental groups. The control oocytes were matured in MEMα medium contains 5% FCS, 7.5 Iu hCG and 100 mIU rFSH. In the experimental groups, immature oocytes were matured in this maturation medium and different amount of phosphodiesterase. Oocyte of each group incubated for 24 hours in 37 C° and 5% CO2. After 24 hours, the activated immature oocytes were classified as GV when the germinal vesicle was present, as GVBD when GV was breakdown and metaphase Π (M Π) when first polar body was extruded.
 Results: The percentage of oocytes remained in GV stage in the control, the first group (80nIu/µu PDEI type4) and 8th group (0.5 nIu/µu PDEI type4) were 18.5, 32.5 and 7.5 percent, respectively (p<0.01). The percentage of in vitro maturation in the control, the first and 8th group were 60.7 ,10 and 77 percent, respectively (p< 0.01).
Conclusion: This study showed that PDEI (type4) enhanced in vitro maturation of immature NMRI mouse strain oocytes and the 0.5 nIu/µu of PDEI (type4) is the best dose.