Endothelium-dependent gender differences in responsiveness of rat aortic smooth muscle to reduction in extracellular magnesium and sodium ions.

Possible gender differences in contractile responses to reduction in extracellular Mg2+ ([Mg2+]0) and [Na+]0 in isolated aortic rings and strips from adult rats were investigated. In consonance with our previous studies, [Mg2+]0 withdrawal (0 mM Mg2+) and reduction in [Na2+]0 (total = 84 mM Na+) by replacement of NaCl with isosmolar amounts of sucrose in normal Krebs-Ringer bicarbonate (NKRB) induced significant increases of basal tone of aortic rings and strips in male, but not in female, rats. However, such tension development was observed in endothelium-denuded aortic preparations isolated from both sexes. No effects of indomethacin (10(-5) M) were found in any of the tissues tested. Adding 1.2 mM MgSO4 to the Mg2+ and Na(+)-deficient incubation media relaxed the tension increase to a normal basal level. The endothelium-dependent vasodilator responses to acetylcholine (10(-10) - 10(-6) M) of aortic rings from male or female rats in NKRB were not different. These results suggest that: (1) as in vascular smooth muscle cells, Mg2+ plays an important role in Ca2+ homeostasis in endothelial cells, probably via Na(+)-Ca2+ exchange and (2) sex steroid hormones may influence contractile responses of vascular smooth muscle by modifying endothelium function through such Mg(2+)-regulated internal Na(2+)-dependent Ca2+ entry.