Effect of Magnesium Sulfate on the Vascular Actions of Norepinephrine and Angiotensin II

ABSTRACT

Magnesium sulfate is used for seizure prophylaxis in patients with preeclampsia. It also has significant effects on calcium metabolism and could, therefore, alter the pressor response to calcium-dependent vasoconstrictors. The present in vivo rat study examined the effect of magnesium sulfate to alter the pressor response to norepinephrine (NE) and angiotensin II (A II). Magnesium doses were chosen to approximate those used in treating preeclampsia. NE resulted in a significant rise in mean arterial pressure (ΔMAP, 46 ± 3.7 mmHg; p <0.001). AII also resulted in a significant rise in MAP (ΔMAP, 23 ± 3.6 mmHg, p <0.02). Magnesium sulfate alone had no significant effect on MAP but attenuated the pressor response to both NE (ΔMAP, 16 ± 1.5 mmHg) and A II (ΔMAP, 12 ± 2.5 mmHg). After discontinuation of the magnesium sulfate infusion, the control pressor responses to NE and A II were again seen (ΔMAP, 39 ± 3.5 mmHg and ΔMAP, 28 ± 4.2 mmHg, respectively). Although magnesium sulfate is not a primary antihypertensive agent, it may have effects on blood pressure by attenuating the actions of circulating vasoconstrictors.