Geldanamycin augments nitric oxide production and promotes capacitation in boar spermatozoa

Sperm capacitation and the acrosome reaction are fundamentally important to fertilization. Nitric oxide (NO) has been shown to have various functions in male reproduction. This work investigates whether boar sperm can generate NO, as well as the effects of NO and geldanamycin (GA), a heat-shock protein 90 (HSP90)-specific inhibitor, on the capacitation of boar spermatozoa. Observations showed that porcine sperm produced low levels of NO under non-capacitating conditions. However, the NO concentration almost doubled under capacitating conditions (P < 0.001). Treatment with NG-nitro-l-arginine methyl ester (l-NAME) reduced the production of NO by 30–40% in capacitating sperm (P < 0.05). GA treatment increased it by 23–75% in a dose-dependent manner (P < 0.05). l-NAME treatment reduced the percentage of sperm undergoing the acrosome reaction, whereas sodium nitroprusside, an NO-releasing compound, and GA treatment increased the percentage of sperm undergoing the acrosome reaction (P < 0.05). GA treatment promoted the production of NO and the acrosome reaction. The increase in NO production by GA treatment was similar to that caused by the calcium ionophore, A23187, suggesting that the GA-induced acrosome reaction may be triggered by an increase of the intracellular calcium concentration. The signaling pathway involved in GA-mediated NO production and its biological function in fertilizing boar spermatozoa will be elucidated in further studies.