INFLUENCE OF OXYGEN-TENSION ON REACTIVE OXYGEN SPECIES PRODUCTION ANDHUMAN SPERM FUNCTION

Human spermatozoa were exposed to the reduced form of nicotinamide ade nine dinucleotide phosphate (NADPH) to stimulate endogenous production of reactive oxygen species (ROS). They were incubated under a gas pha se of 5% CO2/90% N-2/5% O-2, or 5% CO2/95% air (20% O-2) to investigat e whether a lower than atmospheric oxygen tension in the gas phase of the incubator limited the endogenous production of ROS by human sperma tozoa and thus was able to reduce the cytotoxic effects of ROS on sper m function. Exposure of human spermatozoa to exogenous NADPH induced a n 8-fold higher production of superoxide anion under ambient vs. low o xygen tension. This marked difference in the stimulation of superoxide anion generation was associated with significantly different sperm mo tility parameters, according to the oxygen tension in the gas phase of the incubator. Whereas under 5% oxygen the percentage of motile sperm atozoa was unaffected by the presence of NADPH, all of the motility pa rameters recorded under an atmosphere of 5% CO2 in air were dramatical ly affected, not only compared to their respective controls, but also compared to the motility parameters observed under low oxygen tension. The presence of superoxide dismutase plus catalase protected spermato zoa against the toxic effects of NADPH, confirming a cause/effect rela tionship between the increased superoxide production and reduced sperm function. Even at a concentration of NADPH which did not alter the pe rcentage of motile spermatozoa, hyperactivated motility and acrosome r eaction were significantly lower under an atmosphere of 5% CO2 in air compared to a gas phase of 5% CO2/90% N-2/5% O-2. These results sugges t that there is an advantage in using 5% O-2 rather than 20% O-2 in th e gas phase of the incubator to prevent the excessive production of RO S by spermatozoa and related alterations of sperm functions. This may be of clinical value in fertilization programmes.