Possible contributions of reactive oxygen species and mitogen-activated protein kinase to renal injury in aldosterone/salt-induced hypertensive rats

Studies were performed to test the hypothesis that reactive oxygen species (ROS) and mitogen-activated protein kinase (MAPK) contribute to the pathogenesis of aldosterone/salt-induced renal injury. Rats were given 1% NaCl to drink and were treated with one of the following combinations for 6 weeks: vehicle (0.5% ethanol, SC, n = 6); aldosterone (0.75 mug/H, SC, n = 8); aldosterone plus a selective mineralocorticoid receptor antagonist; eplerenone (0.125% in chow, n = 8); aldosterone plus an antioxidant; and tempol (3 mmol/L in drinking solution, n = 8). The activities of MAPKs, including extracellular signal-regulated kinases (ERK)1/2, c-Jun-NH2-terminal kinases (JNK), p38MAPK, and big-MAPK-1 (BMK1) in renal cortical tissues were measured by Western blot analysis. Aldosterone-infused rats showed higher systolic blood pressure (165 +/- 5 mm Hg) and urinary excretion of protein (106 +/- 24 mg/d) than vehicle-infused rats (118 +/- 3 mm Hg and 10 +/- 3 mg/d). Renal cortical mRNA expression of p22phox, Nox-4, and gp91phox, measured by real-time polymerase chain reaction, was increased in aldosterone-infused rats by 2.3, 4.3, and 3.0-fold, respectively. Thiobarbituric acid-reactive substances (TBARS) content in renal cortex was also higher in aldosterone (0.23 +/- 0.02) than vehicle-infused rats (0.09 +/- 0.01 nmol/mg protein). ERK1/2, JNK, and BMK1 activities were significantly elevated in aldosterone-infused rats by 3.3, 2.3, and 3.0-fold, respectively, whereas p38MAPK activity was not changed. Concurrent administration of eplerenone or tempol to aldosterone-infused rats prevented the development of hypertension (127 +/- 2 and 125 +/- 5 mm Hg), and the elevations of urinary excretion of protein (10 +/- 2 and 9 +/- 2 mg/day) or TBARS contents (0.08 +/- 0.01 and 0.11 +/- 0.01 nmol/mg protein). Furthermore, eplerenone and tempol treatments normalized the activities of ERK1/2, JNK, and BMK1. These data suggest that ROS and MAPK play a role in the progression of renal injury induced by chronic elevations in aldosterone.