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High sodium intake causes cardiac hypertrophy independently of increases in blood pressure. Aldosterone is synthesized in extraadrenal tissues such as blood vessels, brain, and heart. Effects of 8 weeks of high sodium intake on cardiac aldosterone synthesis, as well as cardiac structure, mass, and aldosterone production, levels of mRNA coding for aldosterone synthase (CYP11B2) and the angiotensin II AT1 receptor, were studied in normotensive Wistar-Kyoto (WKY) rats. Isolated rat hearts were perfused for 2 hr, and the perfusate was analyzed by high-performance liquid chromatography and mass spectrometry. Aldosterone synthase activity was estimated from the conversion of 14Cdeoxycorticosterone to 14Caldosterone. Levels of mRNA for CYP11B2 and AT1 receptor were determined by competitive polymerase chain reactions. A high sodium intake for 8 weeks produced left ventricular hypertrophy without elevation of blood pressure. Plasma aldosterone concentrations and plasma renin concentrations were decreased by high sodium intake. Aldosterone production, activity of aldosterone synthase, and expression of mRNA for CYP11B2 and AT1 receptor were increased in hearts of rats with high sodium intake. These results suggest that high sodium intake increases cardiac aldosterone synthesis, which may contribute to cardiac hypertrophy independently of the circulating renin-angiotensin-aldosterone system.
Takeda et al. (Mon,) studied this question.