DIETARY MAGNESIUM SUPPLEMENTATION MODIFIES BLOOD-PRESSURE AND CARDIOVASCULAR FUNCTION IN MINERALOCORTICOID-SALT HYPERTENSIVE RATS BUT NOT IN NORMOTENSIVE RATS

The purpose of this study was to determine the effect of dietary magne sium supplementation on blood pressure and cardiovascular function of Sprague-Dawley normotensive and mineralocorticoid-salt (DOCA-salt) hyp ertensive rats. The rats were pair-fed for 5 wk a purified diet contai ning either a normal or magnesium-supplemented diet (1.5 or 10 g/kg di et). Magnesium supplementation significantly lowered blood pressure le vels in hypertensive rats, but not in normotensive rats. Heart rate wa s not affected in either group. The blood pressure-lowering effect of magnesium supplementation in DOCA-salt hypertensive rats was associate d with a lower in vivo cardiovascular reactivity to norepinephrine and angiotensin II. Norepinephrine reactivity in isolated aortae from DOC A-salt hypertensive rats was not modified by magnesium supplementation . However, endothelium-dependent relaxation to acetylcholine was impro ved and could be related to the release of endothelial relaxant factor s. Magnesium supplementation did not affect cardiac hemodynamics in is olated heart from either normotensive or DOCA-salt hypertensive rats. Furthermore, no protective effects upon myocardial ischemia and ventri cular arrhythmias were demonstrated. These findings suggest that the l owering effect of magnesium supplementation on blood pressure in hyper tensive rats may be related to a vascular effect of magnesium that red uces vascular tone. Mechanisms related to the pathophysiological devel opment of mineralocorticoid-salt hypertension may be involved.