Cyclical changes in sperm volume during in vitro incubation under capacitating conditions: a novel boar semen characteristic

The osmotic reactivity of boar spermatozoa during incubation in vitro was s tudied using a hypo-osmotic swelling test in conjunction with electronic me asurement of cell volume. Sperm populations showed fluctuations in both iso -osmotic cell volume and hypo-osmotic volume response that fitted mathemati cal models for periodicity. Significant differences of frequency and amplit ude were observed during sperm incubation under capacitating conditions as compared. with those under noncapacitating conditions. In addition, differe nt boars showed specific differences in their fluctuation characteristics u nder capacitating conditions. During incubation under capacitating conditio ns, a decrease in osmotic reactivity was observed that correlated with a de crease in motility, while the absolute value of the earliest maximum of the osmotic-induced response correlated with an increase in the proportion of discharged acrosomes. The time course of the cyclical behaviour of osmotic reactivity may be a useful parameter for assessing boar sperm response to c apacitating conditions.