Effects of low concentrations of nitric oxide on the zona pellucida binding ability of human spermatozoa

Objective: To investigate the direct effects of sodium nitroprusside. a nitric oxide donor, on the Fertilizing ability of human spermatozoa in vitro. Design: Prospective, controlled in vitro study. Setting: IVF Unit, Medical College Hospital. Patient(s): Women undergoing conventional IVF. Intervention(s): Human spermatozoa samples were incubated with a nitric oxide donor and a nitric oxide quencher, carboxy-imidazolineoxyl N-oxides. Main Outcome Measure(s): The capacitation and the acrosome reaction rates were determined by chlortetracycline assay. Sperm zona pellucida binding and sperm penetration into oocytes were determined using the hemizona assay and the human aged zona-free oocyte sperm penetration assay. Result(s): High concentrations of sodium nitroprusside (10(-3) and 10(-5) hi) inhibited sperm motility and viability. In contrast, low concentrations of sodium nitroprusside (10(-7) and 10(-8) M) did not affect motility and resulted in increased capacitation (47 +/- 6% at 10(-7) M, 42 +/- 6% at 10(-8) M, and 24 +/- 4% in controls, respectively, P<0.01). A twofold increase in the hemizona index occurred compared to the matched control. However, low levels of sodium nitroprusside treatment did not affect the acrosome reaction and human zona-free oocyte sperm penetration rates. Conclusion(s): Low concentrations of nitric oxide may have some physiologic role in fertilization through the enhancement of capacitation and zona pellucida binding but not by the induction of the acrosome reaction or the facilitation of penetration into oocytes. (C) 1998 by American Society for Reproductive Medicine.