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To investigate the effects of reactive oxygen species (ROS) on capacitation, acrosome reaction in human spermatozoa. Human spermatozoa were incubated with xanthine-xanthine oxidase (X-XO), H2O2, sodium nitroprusside (SNP) or lymphocyte. Otherwise, spermatozoa were incubated under low O2 (5 ％) condition. Chlortetracycline (CTC) staining was conducted to assess capacitation and acrosome reaction. Analysis of lipid peroxidation was done by spectrophotometric determination of malondialdehyde (MDA) production in spermatozoa. H2O2, X-XO, SNP and lymphocyte treatment significantly increased capacitated spermatozoa within 1 h of incubation. There was no significant difference in capacitation between low- and high O2 groups. In the presence of low concentration of H2O2, lipid peroxidation decreased significantly. However, under the high concentration of H2O2, lipid peroxidation significantly increased at the end of incubation compared to control. In the presence of high concentration of lymphocytes, lipid peroxidation significantly increased compared to control at 1hr of incubation. There was no significant difference in lipid peroxidation according to O2 concentration examined. Acrosome reaction (AR) was evaluated by CTC staining after the progesterone challenge. In all ROS groups, AR increased compared to control. The X(100 μM) - XO (100mIU) system was the most potent to induce AR. Taken together, it suggested positive control of AR by ROS and the positive relationship between the lipid peroxidation and AR. The early onset of capacitation in the presence of ROS suggest that ROS might be a positive regulator of sperm capacitation and hyperactivation.
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