Magnesium sulphate infusion suppresses the cardiac release of noradrenaline during a handgrip stress test.

Background: Magnesium has several important cardiovascular effects, but its effect on cardiac sympathetic efferent neuron activity has not been clarified.

Objectives: To examine the effect of magnesium sulphate infusion on cardiac sympathetic efferent postganglionic neuronal liberation of noradrenaline.

Patients And Methods: Twenty-two patients who underwent cardiac catheterization were randomly allocated to the control group or the magnesium group. Plasma noradrenaline and adrenaline concentrations in the aorta and the coronary sinus were measured. Noradrenaline or adrenaline release from the heart was calculated by dividing the difference in noradrenaline or adrenaline concentration between the aorta and the coronary sinus by that of the aorta. After baseline blood sampling, the control patients and the patients in the magnesium group received intravenous infusion of saline or magnesium sulphate (10 mmol). All patients were then subjected to 3 min of handgrip exercise stress test to augment sympathetic efferent neuronal activity, and the blood sampling was repeated.

Results: Although blood pressure was increased by the handgrip stress test, there were no differences in heart rate and blood pressure between the two groups, both at baseline and during the handgrip stress test. The plasma noradrenaline and adrenaline concentrations and noradrenaline or adrenaline release from the heart did not differ between the two groups in the baseline condition. However, the handgrip stress increased plasma noradrenaline concentrations and the cardiac noradrenaline release was increased in the control group, whereas the cardiac noradrenaline release was not increased by the handgrip stress in the magnesium group (P<0.02).

Conclusions: These data indicate that magnesium sulphate infusion suppresses the release of catecholamines by the heart, which is an indirect index of sympathetic efferent neuronal activity.