Effect of age on in vitro magnesium modulation of vascular reactivity in the rat aorta.

Vascular reactivity and the effect of various magnesium (Mg) concentrations on it, were studied in aortic rings from adult (4-month-old) and aged (24-month-old) male Sprague-Dawley rats. Contraction induced by CaCl2 of the aortae incubated in high potassium PSS containing 1.2 mM Mg was greater in aged than in adult rats. Low Mg (0.1 mM) decreased CaCl2-induced contraction in the aortae from adult rats more than in those from aged rats. High Mg (4.8 mM) attenuated CaCl2-induced contraction in the aged but not in the adult rats. Acetylcholine- and isoproterenol-induced relaxation of the aortae incubated in normal PSS (1.2 mM) was less pronounced in aged than in adult rats, whereas sodium nitroprusside-induced relaxation was similar in both groups. Low Mg did not modify acetylcholine- and sodium nitroprusside-induced relaxation in adult and aged rats. With high Mg, acetylcholine- and sodium nitroprusside-induced relaxation was increased in both groups. The increasing effect of high Mg on acetylcholine-induced relaxation was however greater in aorta from aged rats. Low Mg decreased isoproterenol-induced relaxation in the adult but not in the aged group, whereas high Mg increased it in both groups of rats. When endothelium was intact, Mg-induced relaxation was less in aged than in adult rats. When endothelium was disrupted, relaxation was similar in both groups . Mg Removal produced an endothelium-dependent relaxation, which was significantly lower in the aged rats. In conclusion, the functional alterations of vascular smooth muscle and endothelium observed with aging modify the modulatory role of Mg on aortic responsiveness.