EVIDENCE THAT NITRIC-OXIDE SYNTHASE IS INVOLVED IN PROGESTERONE-INDUCED ACROSOMAL EXOCYTOSIS IN MOUSE SPERMATOZOA

In a recent work, we detected nitric oxide synthase (NO synthase) in t he acrosome and tail of mouse and human spermatozoa by an immunofluore scence technique. Also, NO-synthase inhibitors added during sperm capa citation in vitro reduced the percentage of oocytes fertilized in vitr o, suggesting a role for NO synthase in sperm function. Therefore, in the present study the effect of three NO-synthase inhibitors, N-G-nitr o-L-arginine methyl ester (L-NAME), N-G-nitro-D-arginine methyl ester (D-NAME) and L-N-G-nitro-arginine (NO2-arg), and of a nitric oxide don or, spermine-NONOate, on the progesterone-induced acrosome reaction of mouse sperm was examined. NO-synthase inhibitors were added at 0, 60 or 90 min during capacitation; at 120 min, mouse epididymal spermatozo a were exposed to 15 mu M progesterone for another 15 min. In another set of experiments, different concentrations of spermine-NONOate were added to capacitated spermatozoa for 15 min; in these experiments, pro gesterone was not included. NO2-arg and L-NAME blocked progesterone-in duced exocytosis regardless of the time at which these inhibitors were added. Moreover, D-NAME did not inhibit exocytosis. In contrast, sper mine-NONOate stimulated the acrosomal exocytosis in vitro directly. Th ese results provide evidence that mouse sperm NO synthase participates in the progesterone-induced acrosome reaction in vitro and that nitri c oxide induces this event.