Sapna, S., S. K. Ranjith, and K. Shivakumar. Cardiac fibrogenesis in magnesium deficiency: a role for circulating angiotensin II and aldosterone. Am J Physiol Heart Circ Physiol 291: H436 -H440, 2006. First published February 10, 2006 doi:10.1152/ajpheart.01185.2005.-Mechanisms underlying cardiac fibrogenesis in magnesium deficiency are unclear. It was reported earlier from this laboratory that serum from magnesium-deficient rats has a more pronounced stimulatory effect on cell proliferation, net collagen production, and superoxide generation in adult rat cardiac fibroblasts than serum from rats on the control diet. The profibrotic serum factors were, however, not identified. This study tested the hypothesis that circulating angiotensin II may modulate cardiac fibroblast activity in hypomagnesemic rats. Male Sprague-Dawley rats were pair-fed a magnesium-deficient (0.0008% Mg) or -sufficient (0.05%) diet for 6 days, and the effects of serum from these rats on [3 H]thymidine and [ 3 H]proline incorporation into cardiac fibroblasts from young adult rats were evaluated in the presence of losartan, an angiotensin II type 1 (AT 1) receptor antagonist, and spironolactone, an aldosterone antagonist. Losartan and spironolactone markedly attenuated the stimulatory effects in vitro of serum from the magnesium-deficient and control groups, but the inhibitory effects were considerably higher in cells exposed to serum from magnesium-deficient animals. Circulating and cardiac tissue levels of angiotensin II were significantly elevated in magnesium-deficient animals (67.6% and 93.1%, respectively, vs. control). Plasma renin activity was 61.9% higher in magnesium-deficient rats, but serum angiotensin-converting enzyme activity was comparable in the two groups. Furthermore, preliminary experiments in vivo using enalapril supported a role for angiotensin II in magnesium deficiency. There was no significant difference between the groups in serum aldosterone levels. The findings suggest that circulating angiotensin II and aldosterone may stimulate fibroblast activity and contribute to a fibrogenic response in the heart in magnesium deficiency. cardiac fibroblasts; renin-angiotensin-aldosterone system; magnesium-deficient rats MAGNESIUM PLAYS an important role in maintaining the structural and functional integrity of the cardiovascular system (1, 2, 19). It has been known for a long time that magnesium deficiency produces a cardiomyopathy characterized by focal myocardial necrosis and fibrosis (3, 9). Many theories have been advanced to explain the molecular basis of myocardial damage associated with magnesium deficiency (22). A large body of experimental evidence suggests that increased oxidative stress in the setting of an immunoinflammatory reaction may produce cardiovascular injury in magnesium deficiency (30). Furthermore, alterations in collagen metabolism and fibroblast proliferation rates, reported earlier from this laboratory (12), point to the activation of cardiac fibroblasts in a rodent model of acute magnesium deficienc...
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