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Dietary Magnesium Supplementation Modifies Blood Pressure and Cardiovascular Function in Mineralocorticoid-Salt Hypertensive Rats but Not in Normotensive Rats¹

Laboratoire Physiologie Pharmacie ^* Laboratoire Pharmacologie Médecine, UFR Médecine et Pharmacie, Place St-Jacques, 25030 Besançon Cedex, France

The purpose of this study was to determine the effect of dietary magnesium supplementation on blood pressure and cardiovascular function of Sprague-Dawley normotensive and mineralocorticoid-salt (DOCA-salt) hypertensive rats. The rats were pairfed for 5 wk a purified diet containing either a normal or magnesium-supplemented diet (1.5 or 10 g/kg diet). Magnesium supplementation significantly lowered blood pressure levels in hypertensive rats, but not in normotensive rats. Heart rate was not affected in either group. The blood pressure-lowering effect of magnesium supplementation in DOCA-salt hypertensive rats was associated with a lower in vivo cardiovascular reactivity to norepinephrine and angiotensin II. Norepinephrine reactivity in isolated aortae from DOCA-salt hypertensive rats was not modified by magnesium supplementation. However, endothelium-dependent relaxation to acetylcholine was improved and could be related to the release of endothelial relaxant factors. Magnesium supplementation did not affect cardiac hemodynamics in isolated heart from either normotensive or DOCA-salt hypertensive rats. Furthermore, no protective effects upon myocardial ischemia and ventricular arrhythmias were demonstrated. These findings suggest that the lowering effect of magnesium supplementation on blood pressure in hypertensive rats may be related to a vascular effect of magnesium that reduces vascular tone. Mechanisms related to the pathophysiological development of mineralocorticoid-salt hypertension may be involved.

KEY WORDS: • mineralocorticoid-salt hypertension • magnesium • blood pressure • rats

¹ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

² To whom correspondence should be addressed.

Manuscript received 22 April 1994. Revision accepted 22 September 1994.