Reactive oxygen species are involved in ovulation. The aim of this study was to 
examine gonadotropin regulation of antioxidant enzyme sulfiredoxin (Srx) and 
peroxiredoxin 2 (PRDX2) expressions and modification during the ovulatory 
process in rats. Administration of antioxidants in vivo reduced ovulation rate 
and cumulus expansion. LH treatment increased H(2)O(2) levels within 15 min, 
which, in turn, induced Srx gene expression in cultured preovulatory follicles. 
Treatment of preovulatory follicles with catalase suppressed the stimulatory 
effect of LH on Akt phosphorylation. LH- or H(2)O(2)-stimulated Srx mRNA levels 
were suppressed by inhibitors of antioxidant agents and MAPK kinase. An in vivo 
injection of equine chorionic gonadotropin-human chorionic gonadotropin (hCG) 
stimulated Srx mRNA within 1 h in granulosa but not thecal cells of preovulatory 
follicles. Srx protein levels were stimulated from 3 h post-hCG injection. 
Immunofluorescence analysis revealed that oocytes expressed the Srx protein. 
Furthermore, hCG treatment increased Srx expression in mural granulosa, theca 
and cumulus cells, but the Srx protein was not detected in corpora lutea. Gene 
expression of PRDX2, identified as an Srx-dependent modified enzyme, was 
stimulated by gonadotropins. In situ hybridization analysis demonstrated that 
PRDX2 mRNA was detected in oocytes and theca cells as well as granulosa cells of 
some antral and preovulatory follicles. High levels of PRDX2 mRNA were detected 
in corpora lutea. Total levels of PRDX2 protein were not changed by 
gonadotropins. However, levels of hyperoxidized PRDX2 increased within 2-3 h 
after the hCG injection. Taken together, gonadotropin stimulation of Srx 
expression and PRDX2 modification in the ovary suggest the existence of an 
antioxidant system to maintain H(2)O(2) production and elimination during the 
periovulatory period.