Hypomagnesemia inhibits nitric oxide release from coronary endothelium: protective role of magnesium infusion after cardiac operations.
BACKGROUND
Postoperative hypomagnesemia is common in patients who have undergone cardiac operations and is associated with clinically significant morbidity resulting from atrial and ventricular dysrhythmias. Magnesium supplementation may increase the cardiac index in the early postoperative period.


METHODS
The action of the magnesium cation on coronary vascular reactivity was studied. Segments of canine epicardial coronary artery were suspended in organ chambers to measure isometric force (95% O2/5% CO2, 37 degrees C).


RESULTS
In coronary segments constricted with prostaglandin F2alpha (2 x 10[-6] mol/L), acetylcholine and adenosine diphosphate (10[-9] to 10[-4] mol/L) induced vasodilation in arteries with endothelium (n=10, each group; p < 0.05). Acetylcholine-mediated vasodilation was blocked by NG-monomethyl-L-arginine (10[-4] mol/L) and NG-nitro-L-arginine (10[-4] mol/L), two inhibitors of nitric oxide synthesis from L-arginine (n=10, p < 0.05). The removal of magnesium from the organ chamber solution impaired vasodilation in response to acetylcholine and adenosine diphosphate. However, normal endothelium-dependent vasodilation could be restored by return of magnesium to the bathing solution. Vascular relaxation in response to bradykinin (10[-9] to 10[-6] mol/L), which was found to induce endothelium-dependent vasodilation independent of nitric oxide production, was unaffected by magnesium removal (n=10).


CONCLUSIONS
Hypomagnesemia selectively impaired the release of nitric oxide from the coronary endothelium. Because nitric oxide is a potent endogenous nitro-vasodilator and inhibitor of platelet aggregation and adhesion, hypomagnesemia could promote vasoconstriction and coronary thrombosis in the early postoperative period.
Pearson
P J
PJ
Section of Cardiovascular Surgery, Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55905, USA.
Evora
P R
PR
Seccombe
J F
JF
Schaff
H V
HV
D000109:Acetylcholine / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology; D001920:Bradykinin / Q000494:pharmacology; D002302:Cardiac Output / Q000187:drug effects; D006348:Cardiac Surgical Procedures; D003328:Coronary Thrombosis / Q000209:etiology; D003331:Coronary Vessels / Q000187:drug effects* / Q000378:metabolism; D015237:Dinoprost / Q000494:pharmacology; D004285:Dogs; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D007262:Infusions, Intravenous; D008274:Magnesium / Q000008:administration & dosage / Q000097:blood* / Q000627:therapeutic use; D008297:Male; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D019335:Nitroarginine / Q000494:pharmacology; D010496:Pericardium; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011183:Postoperative Complications; D014661:Vasoconstriction; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation; D014665:Vasodilator Agents / Q000494:pharmacology; D019323:omega-N-Methylarginine / Q000494:pharmacology
D004791:Enzyme Inhibitors; D010975:Platelet Aggregation Inhibitors; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D019335:Nitroarginine; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D000244:Adenosine Diphosphate; D015237:Dinoprost; D019001:Nitric Oxide Synthase; D008274:Magnesium; D000109:Acetylcholine; D001920:Bradykinin