Mg2+-induced vasodilation in human forearm vasculature is inhibited by NG-monomethyl-L-arginine but not by indometacin

We have investigated the mechanism of the vasodilator action of Mg2+ in human forearm resistance vasculature. Venous occlusion plethysmography was used to measure vasodilator responses to Mg2+ infused via the brachial artery in healthy men, and to determine effects on Mg2+ responses of indometacin (an inhibitor of cyclo-oxygenase) and of NG-monomethyl-L-arginine (L-NMMA, an inhibitor of the L-arginine/nitric oxide, L-arg/ NO, pathway). Magnesium sulphate infusion (0.05, 0.1, 0.2 mmol min(-1)) increased plasma Mg2+ concentration to 1.57 +/- 0.16 mmol.l(-1) in venous blood from the infused arm at the highest dose. There was a dose-related increase in forearm blood flow in the infused arm to a maximum of 6.37 +/- 1.37 ml.min(-1).dl forearm(-1) at the highest dose corresponding to an increase of 159 +/- 25% in blood flow relative to the non-infused arm. There was no tachyphylaxis during a second infusion following a 21-min recovery period. Indometacin had no effect on vasodilator responses to Mg2+, whereas L-NMMA inhibited Mg2+ responses (area under the dose-response curve) by 43 +/- 6% (p = 0.0003 by repeated-measures ANOVA). Therefore the L-arg/NO pathway is responsible, in part, for the vasodilator action of Mg2+ in human forearm resistance vasculature. Copyright (C) 2000 S. Karger AG, Basel.