Nitric oxide interacts with the cAMP pathway to modulate capacitation of human spermatozoa

This study aimed to demonstrate nitric oxide production by human spermatozo a and to characterize the interaction between nitric oxide and cAMP-related pathway in the control of human sperm capacitation and protein tyrosine ph osphorylation. Spermatozoa were incubated in Tyrode's medium with or withou t bovine serum albumin (BSA), and nitric oxide was measured with the spin t rap sodium N-methyl-D-glucamine dithiocarbamate. Under noncapacitating cond itions, spermatozoa produced low levels of nitric oxide. However, under cap acitating conditions, prominent nitric oxide adduct signals were obtained a nd a time-dependent increase of nitric oxide production was observed. When spermatozoa were incubated in Tyrode+BSA medium with nitric oxide-releasing compounds, intracellular cAMP concentrations increased to levels higher th an those of spermatozoa incubated in Tyrode + BSA alone. In contrast, incub ation with nitric oxide synthase inhibitors (N-G-nitro-L-arginine methyl es ter or N-G-monomethyl L-arginine) decreased intracellular sperm cAMP concen trations. The inhibitory effect observed with N-G-nitro-L-arginine methyl e ster on capacitation and tyrosine phosphorylation of two sperm proteins (10 5, 81 kDa) was overcome by the presence of cAMP analogs or of a phosphodies terase inhibitor. These results indicate that nitric oxide is produced by c apacitating human spermatozoa and that it may act as a cellular messenger b y modulating the cAMP pathway involved in capacitation and protein tyrosine phosphorylation. (C) 2000 Elsevier Science Inc.