Hydrogen peroxide is involved in hamster sperm capacitation in vitro.

We have investigated the possibility that the generation of hydrogen peroxide (H2O2) by spermatozoa plays a physiological role during capacitation. Capacitation is defined as the incubation period required for fertilization in mammals. Capacitation culminates in an exocytotic event, the acrosome reaction (AR). Mammalian sperm generate H2O2 during aerobic incubation and do not contain catalase, the enzyme that promotes scavenging of H2O2. In the present work we show that added catalase inhibited the AR, while glucose oxidase (GO), an enzyme that generates H2O2, accelerated the onset of the AR. Direct addition of H2O2 also stimulated the AR; catalase inhibited both the stimulation by GO and by H2O2. The onset of the AR was always preceded by the appearance of hyperactivated motility. The stimulation of the AR by H2O2 was manifest 1-2 h after the addition of H2O2. Catalase added at 3 h of incubation was less effective in inhibiting the AR than catalase added at the beginning. Incubation of sperm with catalase prevented the induction of the AR by the membrane-perturbing lipid, lysophosphatidyl choline. Taken together, these results suggest that H2O2 produced by hamster sperm plays a significant role during capacitation, possibly in membrane reorganization to facilitate the fusion that takes place during exocytosis of the acrosomal contents.

Epinephrine decreases the potassium requirements of hamster sperm capacitation: furosemide blocks the effect of epinephrine.

We have investigated the possibility of an interaction between epinephrine and external potassium in the stimulation of the hamster sperm acrosome reaction and in vitro fertilizing ability. We have found that: 1) K+ is required late in capacitation and/or the acrosome reaction, but is not required for penetration of the zona pellucidae, 2) the presence of epinephrine (50 microM) in the capacitation medium lowers the K+ requirements of these processes and 3) furosemide, a cotransport inhibitor, blocks the acrosome reaction, in vitro fertilization, and inhibits the stimulation by epinephrine. These results support the idea that there is an interaction between epinephrine as a stimulus to the secretion of the acrosomal content, and K+ as a mediator of the stimulus signal. They further suggest that K+ influx through the cotransport mechanism occurs during capacitation, that this mechanism is activated late during the process, and that it probably mediates the stimulatory effects of epinephrine. We would like to propose that the activation of passive cation transport mechanisms is a general phenomenon in biological signal transduction.