This study was conducted to investigate the effects of nitric oxide (NO) on human sperm activity, human sperm-oocyte fusion and mouse embryonic development. Results showed that various concentrations of NO synthase blocker, Nω-nitro-L-arginine methyl ester, did not affect sperm cell motility at 0, 1, 2 or 4 hr, respectively. In contrast, sodium nitroprusside (SNP) significantly inhibited sperm cell motility and caused apoptosis. The adversely dose-dependent effect was only observed if SNP was freshly prepared. Adenosine triphosphate reversed the hazardous effect of SNP on sperm activity/viability. Hemoglobin neutralized the adverse effect of SNP. In hemi-zona sperm fusion test, the number of sperm bound to the zona in the presence of 10-4 M SNP was significantly less than the control group. SNP at 10-4 M caused all mouse embryonic development arrest. 46% and 56% of zygote reached the blastocyst stage with the treatment of 10-6 M and 10-8 M SNP, respectively, while the control reached 70%. NO adversely affected human sperm activity, human sperm-zona binding and embryonic development. It would appear that high concentration of NO may potentially decrease fertility.
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