Dietary salt restriction in hyperthyroid rats. Differential influence on left and right ventricular mass

This study assessed the impact of salt restriction on cardiac morphology and biochemistry and its effects on hemodynamic and renal variables in experimental hyperthyroidism. Four groups of male Wistar rats were used: control, hyperthyroid, and the same groups under low salt intake. Body weight, blood pressure (BP), and heart rate (HR) were recorded weekly for 4 weeks. Morphologic, metabolic, plasma, cardiac, and renal variables were also measured. Low salt intake decreased BP in T₄-treated rats but not in controls. Low salt intake reduced relative left ventricular mass but increased absolute right ventricular weight and right ventricular weight/BW ratio in both control and hyperthyroid groups. Low salt intake increased Na⁺/H⁺ exchanger-1 (NHE-1) protein abundance in both ventricles in normal rats but not in hyperthyroid rats, independently of its effect on ventricular mass. Mammalian target of rapamycin (mTOR) protein abundance was not related to left or right ventricular mass in hyperthyroid or controls rats under normal or low salt conditions. Proteinuria was increased in hyperthyroid rats and attenuated by low salt intake. In this study, low salt intake produced an increase in right ventricular mass in normal and hyperthyroid rats. Changes in the left or right ventricular mass of control and hyperthyroid rats under low salt intake were not explained by the NHE-1 or mTOR protein abundance values observed. In hyperthyroid rats, low salt intake also slightly reduced BP and decreased HR, proteinuria, and water and sodium balances.