Figure 1. Vascular Effects of Magnesium Sulfate.

Magnesium is a potent vasodilator of uterine and mesenteric arteries, and aorta, but has minimal effect on cerebral arteries. In vascular smooth muscle, magnesium competes with calcium for binding sites, in this case for voltage-operated calcium channels (VOCC). Decreased calcium channel activity lowers intracellular calcium, causing relaxation and vasodilation. In endothelium, magnesium has been shown to increase production of prostaglandin I₂ (through unknown mechanisms), which in turn decreases platelet aggregation. Magnesium also increases NO production causing vasodilation.