Effect of nitric oxide on boar sperm motility, membrane integrity, and acrosomal status during semen storage

Nitric oxide (NO) is a major gasotransmitter involved in several physiological processes of male reproduction. There is, nevertheless, little information concerning the role of NO during semen storage. The aim of this study was to evaluate the effect of NO on boar semen stored at 17oC for 72 h. For this purporse, sperm samples were treated with 0.625, 1.25, 2.5, 5, and 10 mM aminoguanidine (AG) or Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME), a selective and non-selective NO synthase (NOS) inhibitor, respectively. Moreover, sodium nitroprusside (SNP), a NO donor, was used at the dose of 18.75, 37.5, 75, and 150 μM. Sperm motility, membrane integrity, and acrosomal status were evaluated at 0, 4, 24, 48, and 72 h of semen storage. A significant increase of the amplitude of lateral sperm head displacement (ALH), and both curvilinear and straight-line velocity (VCL and VSL, respectively) was observed at 72 h of semen storage in samples treated with 0.625 mM AG, probably because of the antioxidant properties of this NOS inhibitor. Contrarily, 0.625 mM L-NAME showed no effect on boar sperm parameters during the entire period of semen storage. Moreover, AG and L-NAME at 10 mM negatively affected sperm kinetics and acrosome integrity, which may provide further support to the notion that low NO levels are necessary for a normal sperm function. The concentrations of SNP used in this study had mostly no or negative effects on boar sperm parameters during semen storage. In conclusion, the results from this study increase the understanding of the role of NO on boar sperm physiology.