Correspondence: Contribution of Nitric Oxide to Vasodilatation by Substance P in Human Forearm Vessels: Author's Reply

stance P was different; we obtained it from Peptide Research Laboratories, Osaka, Japan whereas theirs was from Clinalfa, Calbiochem-Novabiochem (UK) Ltd, Nottingham, U.K. Although L-NMMA did not inhibit substance P-induced forearm vasodilatation in our study, another group from our laboratory has demonstrated that L-NMMA inhibited substance P-induced coronary vasodilatation in humans but not forearm vasodilatation [3]; the same substance P was used for these two studies. Moreover, we have shown that L-arginine, a substrate of nitric oxide, augments acetylcholine-induced forearm vasodilatation but does not affect substance P-induced vasodilatation [4]. These findings support the notion that substance P-induced vasodilatation is not mediated by nitric oxide, at least in the forearm. Finally, there may be racial differences because Panza et al. [5] from the U.S.A. reported that substance P-induced vasodilatation was inhibited by L-NMMA. It may be necessary to perform experiments with the same protocol after exchanging sources of substance P.