Abstract: [Objective] This study was conducted to characterize the expression pattern of antioxidant enzymes in sheep antral ovarian follicles with different diameters, so as to provide references for clarifying the regulatory mechanism of antioxidant function in ovarian follicles. [Method] The follicular fluids were sampled from sheep antral ovarian follicles with different diameters （large antra ≥ 6.0 mm, medium antra 2.0-6.0 mm, small antra ≤ 2.0 mm). The contents of reactive oxygen species （ROS） and total antioxidant capacity （TAC）, as well as the activities of superoxide dismutase （SOD）, catalase （CAT）, glutathione peroxidase （GPX） and peroxidase （PRDX） were tested using the commercially available reagent kits. Real time fluorescence quantitative PCR （qPCR） assay was used to detect the relative mRNA expression levels of Cu/Zn-SOD, CAT, GPX3 and PRDX6 genes in the theca cells, mural granulosa cells and cumulus cells of small, medium and large antral ovarian follicles. [Result] There were no significant （P>0.05） differences in the contents of TAC and ROS in the follicular fluids of antral ovarian follicles with different diameters. The activities of SOD, GPX and PRDX in the follicular fluids decreased with the increase of ovarian follicle diameters. The small antral ovarian follicles had extremely significantly （P<0.01） higher activities of SOD, GPX and PRDX in the follicular fluids compared to the large antral ovarian follicles. The CAT activity in the follicular fluids elevated with the increase of ovarian follicle diameters. The large and medium antral ovarian follicles had extremely significantly （P<0.01） higher CAT activities in the follicular fluids than the small antral ovarian follicles. The relative mRNA expression levels of Cu/Zn-SOD, GPX3 and PRDX6 genes in the theca cells and mural granulosa cells of the small antral ovarian follicles were extremely significantly （P<0.01） higher than those of the medium and large antral ovarian follicles, while the relative mRNA expression levels of Cu/Zn-SOD, GPX3 and PRDX6 genes in the cumulus cells of the medium antral ovarian follicles were extremely significantly （P<0.01） higher than those of the small and large antral ovarian follicles. The large antral ovarian follicles had extremely significantly （P<0.01） higher relative mRNA expression levels of CAT gene in the theca cells and mural granulosa cells than the small and medium antral ovarian follicles, while the large and medium antral ovarian follicles had extremely significantly （P<0.01） higher relative mRNA expression levels of CAT gene in the cumulus cells than the small antral ovarian follicles. [Conclusion] There was no significant variations in contents of TAC and ROS in sheep antral ovarian follicles with different diameters, but the gene expression levels and the activities of antioxidant enzymes of SOD, CAT, GPX and PRDX in ovarian follicles with different diameters exhibited spatial specificity, indicating that the regulation of antioxidant function in sheep antral ovarian follicles was a synergistic process of multiple factors.

Key words: sheep, antral ovarian follicle, superoxide dismutase, catalase, glutathione peroxidase, peroxidase