Production of NA by endothelial NO-synthase: an in vitro versus in vivo study

Endothelial-derived relaxing factor (EDRF) is secreted by different endothelia in vivo. It is synthesised by endothelial NO-synthase (eNOS). Despite numerous works, its identity is not fully understood. Here the production of NA, a nitroso-arginine, which was shown to be synthesised by brain NO-synthase (bNOS), was studied in eNOS preparations. NA was quantified by reductive differential pulse voltammetry (RDPV) during its irreversible electrochemical transformation to N-hydroxy-arginine (NHA). Using microelectrodes, NA and nitrite were simultaneously measured in pure recombinant eNOS giving similar enzyme activity. NA was detected at the surface of human endothelial cells (HUVEC) and disappeared when D-arginine was introduced in the culture medium. NA production by endothelium tissue was studied in rat corpus cavernosum using voltammetric microelectrodes. NA concentration at the endothelium surface was linked to vasodilatation measured by laser Doppler induced by acetylcholine injection. LNMA ic injection induced NA disappearance. These preliminary new experiments suggested that NA could be the endogenous nitroso-compound presented early as EDRF.