Influence of progesterone on boar sperm capacitation

This research investigates the effect of progesterone (P-4) on boar sperm capacitation. Ejaculated spermatozoa were washed and incubated under capacitating conditions with or without P-4. At different times of incubation samples of sperm were exposed to solubilized zonae pellucidae (ZP) and the degree of capacitation was evaluated by the incidence of zona-induced acrosome reaction (AR). The status of the acrosome was studied by using an FITC-conjugated lectin (Pisum sativum agglutinin; FITC-PSA). The effect of P-4 on the fertilizing ability of semen was then evaluated in an in vitro fertilization system by exposing in vitro matured oocytes to sperm preincubated for 2 or 4 h with or without P-4, under capacitating conditions. PSA staining showed that P-4 does not affect the incidence of spontaneous AR. By contrast, spermatozoa incubated with P-4 showed a higher percentage of AR than controls after the exposure to solubilized ZP. This enhanced reactivity to ZP suggests a direct effect of P-4 on sperm capacitation. The in vitro fertilization assay was consistent with these results demonstrating a higher fertilizing ability in sperm preincubated with P-4 than in controls while the steroid was without effect when added only during the fertilization step. These results demonstrate that P-4 improves the fertilizing ability of boar semen essentially by facilitating the process of capacitation.[...]