Magnesium causes nitric oxide independent coronary artery vasodilation in humans

Objective-To determine how magnesium affects human coronary arteries and whether endothelium derived nitric oxide (EDNO) is involved in the coronary arterial response to magnesium. Design-Quantitative coronary angiography and Doppler flow velocity measurements were used to determine the effects of the nitric oxide synthase inhibitor N-G-monomethyl-L-arginine (L-NMMA) on magnesium induced dilation of the epicardial and resistance coronary arteries. Setting-Hiroshima University Hospital a tertiary cardiology centre. Patients-17 patients with angiographically normal coronary arteries. Interventions-Magnesium sulfate (MgSO4) (0.02 mmol/min and 0.2 mmol/min) was infused for two minutes into the left coronary ostium before and after intracoronary infusion of L-NMMA. Main outcome measures-Diameter of the proximal and distal segments of the epicardial coronary arteries and coronary blood flow. Results-At a dose of 0.02 mmol/min, MgSO4 did not affect the coronary arteries. At a dose of 0.2 mmol/min, MgSO4 caused coronary artery dilation (mean (SEM) proximal diameter 3.00 (0-09) to 3.11 (0.09) mm; distal 1.64 (0.06) to 1.77 (0.07) mm) and increased coronary blood flow (79.3 (7.5) to 101.4 (9.9) ml/min, p < 0.001 v baseline for all). MgSO4 increased the changes in these parameters after the infusion of L-N.MMA (p < 0.001 v baseline). Conclusions-Magnesium dilates both the epicardial and resistance coronary arteries in humans. Furthermore, the coronary arterial response to magnesium is dose dependent and independent of EDNO.