Roles of magnesium ions in vascular relaxation via calcium channel and cyclooxygenase pathway in isolated rat aorta

Abstract

The impact of magnesium (Mg) on vascular tone is mainly due to its calcium antagonist activity resulting in smooth muscle relaxation. The present study was designed to determine the roles of nitric oxide and calcium ions in magnesium -induced vasorelaxation in rats aortic rings. In this study, the aorta contracted with NE (3x10-6M), pre-incubated with cyclooxygenase (COX) and epoxygenase inhibitors, then dose response curve(DRC) made to magnesium sulfate (MgSO4 ) served as a control. On the other hand, the aorta incubated with L-NAME (10 mM) ,nifedipine (10-5M) , indomethacin (10-5M) and clotrimazole (30 mM) for 20 minutes then contracted by nor-epinephrine (NE) and relaxed by MgSO4 doses. Interestingly, L-NAME shifted the DRC of MgSO4 to the left and elevated Emax significantly. Furthermore, p IC50 tended to increase in L-NAME pre-incubated aortic rings. Also, aortic rings that are pre-contracted with 10-6M NE in the absence of calcium ions shifted the DRC to the left but it significantly reduced pIC50. Furthermore, calcium channel blocker (Nifedipine) significantly reduced the relaxatory effects of magnesium ions and it markedly decreased Emax with altering pIC50 values significantly. The present results revealed that indomethacin pre-incubation slightly shifted the curve of MgSO4 to the right, while p IC50 was significantly increased and Emax did not significantly change in clotrimazole pre-incubation. In conclusions, the results of this study suggested that magnesium ions can probably relax aortic smooth muscles , and this is may be returned to in part to nitric oxide ,COX and epoxygenase enzyme pathways.