European Journal of Pharmacolog); 154 (1988) 213-216 213 Elsewer EJP 20200 Short communication Arginine is a physiological precursor of endothelium-derived nitric oxide Harald H.H.W. Schmidt, Heinz Nau 1, Werner Wittfoht 1 J~Srg Gerlach 2, Karl-Ernst Prescher 3, Marcus M. Klein, Feraydoon Niroomand and Eycke BShme * InstltUt fur Pharmakologte, 1 Insntut fur Toxlkologle und Embryonalpharmakologle and : ChJrurgzsche Unwersttatskhmk. UKR V Charlottenburg, Frele Unwersttat Berhn, D-1000 Berhn, and 3 Instttut fur Wasser-, Boden- und Lufthygtene des Bundesgesundhettsamts, D-IO00 Berhn, F R G Received 23 May 1988, accepted 19 July 1988 ATP dose dependently stimulated the formation and release of nitric oxide (NO) from perfused rabbit aorta. L-Canavamne, an irdubitor of various L-arglnlne-utilizing enzymes, abolished basal and ATP-mduced NO formation and release. ATP increased the accumulation of presumably NO-derived NOy m the medium of primary cultures of bovine aortic endothelial cells. 15NO, 15NO~- and 15NO3 formation was found when L-[guamdo-~SNz]argamne was added to the culture medium We conclude that the terminal guanldIno mtrogens of L-argmine are the physiological precursors of endothehum-denved NO. Endothelium; Nitric oxide; L-Argimne I. Introduction The vascular smooth muscle relaxation induced by ATP and other substances is endothelium-de- pendent and mediated by endothelium-derived re- laxing factors (EDRFs; Furchgott, 1984). One EDRF has been identified as being nitric oxide (NO; Palmer et al., 1987; Ignarro et al., 1987). NO induces vascular smooth muscle relaxation due to an interaction with the heme component of solu- ble guanylate cyclase, leading to an increase of cGMP formation (Gerzer et al., 1981; Waldman and Murad, 1987). Iyengar et al. (1987) have demonstrated that NO2, NO 3 and, when mor- pholine was present, N-mtrosomorpholine pro- duced by cultured macrophages were exclusively derived from the terminal guanidino nitrogens of * To whom all correspondence should be addressed InstltUt fur Pharmakologte, FU Berhn, Thlelallee 69-73, D-1000 Berhn 33, F R G L-arginine (ARG). NO is likely to be the nitrosy- lating agent forming N-nitrosomorpholine. NO should then be the primary product of this arginine-utihzing biosynthetic pathway as NO is readily oxidized to NO 2 and NO 3 in neutral aqueous solution and in the presence of 0 2 as cell culture medium. We have proposed a biosynthetic pathway for vascular endothelial cells in which ARG is a physiological precursor of endothelium- derived nitric oxide (EDNO; Schrmdt et al., 1988). 2. Materials and methods 2.1. Detectton of NO release by chemdummescence Male rabbits (New Zealand White, 3.5 kg) were killed, the thoracic aorta was removed and cleaned of fat and connective tissue. The aorta was then cannulated as both ends, mounted vertically in a 25 ml organ bath (37°C) and perfused at 200 ml/h. The bathing and perfusion solution were a 0014-2999/88/$03 50 © 1988 Elsewer Science Pubhshers B V (Biomedical Division)