Effect of magnesium on vascular tone and reactivity in pressurized mesenteric resistance arteries from spontaneously hypertensive rats.

This study examines the effects of magnesium on vascular tone and reactivity in mesenteric resistance arteries from 17-week-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Third-order branches of mesenteric arteries were mounted in a pressurized flow chamber and studied with constant flow and transmural pressure. The mesenteric arteries were perfused extra- and intra-luminally with physiological salt solution containing a normal (1.2 mmol/L), high (4.8 mmol/L), or low (0.15 mmol/L) magnesium concentration. Vascular reactivity to norepinephrine and vasopressin was examined when the agonists were applied extraluminally. High magnesium increased lumen diameter and decreased media thickness whereas low magnesium decreased lumen diameter and increased media thickness in mesenteric arteries from both SHR and WKY rats. The effects of magnesium on vascular tone were less in arteries from SHR compared with normotensive controls (p < 0.05). Low magnesium potentiated norepinephrine-induced vasoconstriction in SHR (p < 0.001) but not in WKY. Low magnesium did not modify vasopressin-induced vasoconstriction in either SHR or WKY. High magnesium attenuated vasopressin- and norepinephrine-induced vasoconstriction in SHR (p < 0.01), whereas high magnesium attenuated only norepinephrine-induced vasoconstriction in WKY (p < 0.001). These data suggest that magnesium has differential modulatory effects on vascular tone and reactivity in mesenteric resistance arteries of SHR and WKY. Magnesium may play an important role in the modulation of peripheral resistance in hypertension.