Influence of oxygen tension on function of isolated spermatozoa from ejaculates of oligozoospermic patients and normozoospermic fertile donors

Oxygen radical generation is known to be detrimental to sperm function. An example of a reactive oxygen species-associated male pathology is oligozoospermia in which fertilization and pregnancy rates are low in in-vitro fertilization (IVF) programmes. As the extent of the modifications induced by reactive oxygen species (ROS) depends on several factors, notably from oxygen tension in the incubation medium, the aim of this study was to examine the influence of a low (5%) rather than atmospheric (20%) oxygen tension in the incubator gas phase on the function of Percoll-selected spermatozoa from ejaculates of oligozoospermic patients and normozoospermic fertile donors. After incubation for several hours in a gas phase of either 5% CO2/90% N2/5% O2 or 5% CO2/95% air (20% O2), none of the parameters investigated, e.g. movement characteristics, potential of spermatozoa to acquire hyperactivated motility, to undergo the acrosome reaction when challenged with a calcium ionophore and to fuse with zona-free hamster oocytes, was significantly different between the two oxygen tensions in fertile donors. In contrast, among oligozoospermic patients, the motility parameters, the percentage of hyperactivated motility and of induced-acrosome reaction were significantly improved under a gas phase of 5% O2 compared with those observed under an atmosphere of 20% O2 (P < 0.05). Exposure to 5% rather than 20% oxygen tension also induced a significant increase in the percentage of penetration of zona-free hamster eggs after capacitation for 17 h, but no difference was found in the mean number of bound spermatozoa per oocyte. After incubation for 24 h, a significantly higher survival rate was observed under 5% compared with 20% oxygen tension. These results show that the use of a low oxygen tension rather than air might improve spermatozoan competence of oligozoospermic patients during IVF programmes.