SUPEROXIDE ANION PRODUCTION BY HUMAN SPERMATOZOA AS A PART OF THE IONOPHORE-INDUCED ACROSOME REACTION PROCESS

The involvement of superoxide anion (O-2(o-)) in human sperm capacitat ion and/or acrosome reaction was investigated. Addition of superoxide dismutase (SOD) to the medium at the beginning of the capacitation pro cess or 15 min before induction of the acrosome reaction, decreased th e level of ionophore-induced acrosome reaction. Hyperactivation was un affected by the presence of SOD during the capacitation process. Addit ion of calcium ionophore to the sperm suspension increased production of O-2(o-) by the spermatozoa by four to five-fold and induced the acr osome reaction. In the presence of SOD, superoxide anion could not be detected in the medium and the rate of induced-acrosome reaction was d ecreased greatly. The presence of an inhibitor of protein kinase C inh ibited the production of O-2(o-) in the medium and reduced the induced -acrosome reaction. The production of O-2(o-) and the acrosome reactio n were also increased by exposure of spermatozoa to 12-myristate 13-ac etate phorbol ester, a specific activator of protein kinase C. While t he level of spontaneous acrosome reaction was not increased by the dir ect addition of O-2(o-) to the medium, its presence induced the releas e of unesterified fatty acids from membrane phospholipids. These findi ngs suggest that the production of O-2(o-) by spermatozoa could be inv olved in the ionophore-induced acrosome reaction, possibly through the de-esterification of membrane phospholipids. However, this production of superoxide anion is not sufficient on its own to induce the acroso me reaction.