Human sperm endothelial nitric oxide synthase expression: correlation with sperm motility

Objective: To characterize the pattern of endothelial nitric oxide synthase (eNOS) expression on human spermatozoa and to determine whether sperm eNOS expression correlates with sperm function. Design: Prospective, observational study. Setting: University infertility clinic. Patient(s): Twelve nonazoospermic infertile men. Intervention(s): Semen samples (n = 12) obtained from nonazoospermic infertile men were fractionated on discontinuous Percoll gradients. Endothelial nitric oxide synthase staining on spermatozoa was correlated with sperm motility in Percoll gradient–fractionated spermatozoa. Endothelial nitric oxide synthase protein was detected with the use of a previously characterized monoclonal antibody. Control slides were incubated with preabsorbed antibody or mouse immunoglobulin G. Main Outcome Measure(s): Localization of eNOS on human spermatozoa and correlation between the pattern of sperm eNOS expression and sperm motility. Result(s): Morphologically normal spermatozoa exhibited postacrosomal and equatorial eNOS immunostaining. However, abnormally shaped spermatozoa often exhibited aberrant staining (in the midpiece and/or head region). A significant negative correlation was observed between the percentage of sperm with aberrant eNOS immunostaining and the percentage of motile sperm ( r = −.46). Conclusion(s): The specific localization of eNOS to human spermatozoa suggests that nitric oxide may be involved in normal sperm physiology. However, aberrant patterns of sperm eNOS expression are associated with decreased sperm motility, possibly through the generation of excessive cytotoxic oxidants.