LOW-LEVELS OF NITRIC-OXIDE PROMOTE HUMAN SPERM CAPACITATION IN-VITRO

The influence of nitric oxide on human sperm hyperactivation and capac itation, as well as its mechanism of action and its possible origin fr om spermatozoa were studied. Percoll-washed spermatozoa from healthy v olunteers were incubated in Ham's F-10 medium supplemented or not with the nitric oxide-releasing agents, diethylamine-NONOate or spermine-N ONOate, in combination or not with superoxide dismutase or catalase (s cavengers for the superoxide anion and for hydrogen peroxide, respecti vely), or with sodium nitrate, sodium nitrite, or preincubated NONOate s. Sperm hyperactivation, capacitation, and nitric oxide synthase acti vity were determined. High concentrations (0.3 to 1 mM) of NONOates re duced sperm motility. However, a lower concentration (0.1 mM) of the t wo NONOates had no effect on the percentage of sperm motility or of hy peractivation but resulted in a significant increase in sperm capacita tion (24% +/- 4%) when compared to that of control spermatozoa (Ham's F-10 alone, 12% +/- 2%). Nitric oxide released by the NONOates appeare d responsible for this effect because sodium nitrate or nitrite or pre incubated NONOates (to exhaust the formation of nitric oxide) had no i nfluence on sperm capacitation. Catalase, but not superoxide dismutase , abolished the capacitating action of the NONOates. No nitric oxide s ynthase activity was detected in spermatozoa, whether they were in the ir basal state or already capacitated. Furthermore, the nitric oxide s ynthetase inhibitor L-N-G nitroarginine methyl ester did not block spe rm capacitation induced by fetal cord serum ultrafiltrate, It is there fore concluded that, although spermatozoa do not possess detectable ni tric oxide synthase activity, low levels of nitric oxide induce human sperm capacitation, and this action likely involves hydrogen peroxide.