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 (MgSO(4)) (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, MgSO(4) did not affect the coronary arteries. At a dose of 0.2 mmol/min, MgSO(4) 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). MgSO(4) increased the changes in these parameters after the infusion of L-NMMA (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.