Systemic and regional hemodynamic effect of acute magnesium administration in the normotensive and hypertensive state

Recent interest has focused on the role that Mg2+ may play in blood pressure (BP) regulation and in hypertension. The acute effect of intravenous Mg2+ as well as vehicle administration on systemic and regional hemodynamics was determined in both normotensive rats and in rats made hypertensive by uninephrectomy followed by deoxycorticosterone acetate and salt excess (DOCA-salt). Systemic and regional hemodynamics were determined by the radioactive microsphere method in the conscious and unrestrained rat prior to and 1 h following either Mg2+ or vehicle administration. Mg2+ administration significantly increased serum Mg2+ levels in both the normotensive and DOCA-salt hypertensive rats (1.4 +/- 0.02 to 3.5 +/- 0.04 and 1.7 +/- 0.06 to 4.9 +/- 0.4 mEq/l, respectively, both p less than 0.01). The DOCA-salt rats had a significantly greater baseline mean BP, total peripheral resistance (TPR), and heart rate (HR), when compared to the normotensive rats. In the normotensive rats, neither Mg2+ or vehicle administration had any effect on either mean BP or HR. In the DOCA-salt hypertensive rats, vehicle administration had no effect on any systemic hemodynamic parameter. However, in marked contrast, Mg2+ administration significantly decreased mean BP, HR and TPR while not changing cardiac output or index. In both the normotensive and DOCA-salt hypertensive rats vehicle administration did not result in any significant regional organ vascular resistance changes. However, in the normotensive rats, Mg2+ administration significantly decreased vascular resistance in the heart and in the DOCA-salt hypertensive rats Mg2+ administration significantly decreased vascular resistance in the heart, muscle and skin while increasing vascular resistance in the stomach. In conclusion, acute Mg2+ administration significantly decreases blood pressure by peripheral vasodilation in DOCA-salt hypertensive but not in normotensive rats. In addition, acute Mg2+ administration results in a redistribution of blood flow to the heart in both the hypertensive and normotensive state as well as also possibly to the kidney and brain in the hypertensive state. The antihypertensive effect of Mg2+ in the DOCA-salt hypertensive rats as well as the prominent coronary vasodilation seen in both the normotensive and hypertensive rats may have important clinical implications.