Abstract
Capacitation and acrosome reaction are of fundamental importance in the fertilization of oocyte by spermatozoon. The process of capacitation consists of a series of functional and biophysical modifications that render the ejaculated spermatozoa competent for fertilization of the oocyte. Nitric oxide (NO) has been shown to have multifunction in male reproduction system. The objectives of the present study were to investigate whether boar spermatozoa can generate NO and the effects of NO and heat-shock protein 90 (HSP90) on the capacitation of boar spermatozoa. The major results were as follows: Boar spermatozoa possess endothelial nitric oxide synthase (eNOS) in the acrosome and middle piece, and spermatozoa can generate NO. Under noncapacitating conditions, spermatozoa produced low levels of NO. However, there was an up to 2-fold increase of NO generation under capacitating conditions (P<0.001). When boar spermatozoa were incubated with capacitation medium in the presence of NOS inhibitor (NG-nitro-L-arginine methyl ester, L-NAME) or geldanamycin (GA) for 4 h, L-NAME treatment reduced 30% to 40% of NO production in capacitating spermatozoa (P<0.05). However, GA promoted 23% to 75% of NO production in a dose-dependent manner (P<0.05). When spermatozoa were capacitated in the presence or absence of NO-releasing compound (SNP), L-NAME or GA, and then the percentage of acrosome reaction induced by calcium ionophore (A23187) was determined. The results indicated that L-NAME decreased the percentage of acrosome reaction, whereas SNP and GA increased the percentage of acrosome reaction (P<0.05). Since GA treatment did not decrease but increase NO production as expected, HSP90 may not directly involve in regulating NOS activity during boar spermatozoa capacitation in vitro. On the other hand, the phenomenon of increasing NO production is similar to the effect of A23187, we suggest that acrosome reaction induced by GA may be triggered the increase of intracellular calcium concentration and NO production.