Koji Ito1, Yoshitaka Hirooka, Kenji Sunagawa. 1. Department of Cardiovascular Medicine, Kyushu University Graduate School of Medical Sciences, Higashi-ku, Fukuoka, Japan.
Abstract
OBJECTIVES: In a pressure overload model, sympathetic activity is augmented in response to salt intake. Mineralocorticoid receptors and epithelial Na channels (ENaCs) are thought to contribute to Na-processing, but the underlying mechanism is unknown. Here, we investigated the contribution of the brain mineralocorticoid receptor- ENaC pathway to salt-induced sympathetic activation in a pressure overload model. METHODS AND RESULTS: Aortic banding was performed to produce a mouse pressure overload model. Four weeks after aortic banding (AB-4), left-ventricular (LV) wall thickness was increased without a change in percentage fractional shortening (%FS). Sympathetic activity increased in response to a 5-day high-salt diet in AB-4, but not in Sham-4. Brain mineralocorticoid receptor, alphaENaC, and angiotensin II type 1 receptor (AT1R) expression levels were greater in AB-4 than in Sham-4. The increase in sympathetic activity and in the expression of these proteins was blocked by intracerebroventricular (ICV) infusion of eplerenone, a mineralocorticoid receptor blocker. In another protocol, AB-4 mice were fed a high-salt diet (AB-H) for 4 additional weeks. At 4 weeks, %FS was decreased and sympathetic activity was increased in AB-H compared with Sham. Expression of mineralocorticoid receptors and AT1R in the brain was higher in AB-H than in Sham. ICV infusion of eplerenone in AB-H attenuated salt-induced sympathoexcitation and the decreased %FS. ICV infusion of eplerenone also decreased brain AT1R expression. CONCLUSIONS: These findings indicate that activation of brain alphaENaC and AT1R through mineralocorticoid receptors contributes to the acquisition of Na sensitivity to induce sympathoexcitation. Therefore, high salt intake accelerates sympathetic activation and LV systolic dysfunction in a pressure overload model.
OBJECTIVES: In a pressure overload model, sympathetic activity is augmented in response to salt intake. Mineralocorticoid receptors and epithelial Na channels (ENaCs) are thought to contribute to Na-processing, but the underlying mechanism is unknown. Here, we investigated the contribution of the brain mineralocorticoid receptor- ENaC pathway to salt-induced sympathetic activation in a pressure overload model. METHODS AND RESULTS: Aortic banding was performed to produce a mouse pressure overload model. Four weeks after aortic banding (AB-4), left-ventricular (LV) wall thickness was increased without a change in percentage fractional shortening (%FS). Sympathetic activity increased in response to a 5-day high-salt diet in AB-4, but not in Sham-4. Brain mineralocorticoid receptor, alphaENaC, and angiotensin II type 1 receptor (AT1R) expression levels were greater in AB-4 than in Sham-4. The increase in sympathetic activity and in the expression of these proteins was blocked by intracerebroventricular (ICV) infusion of eplerenone, a mineralocorticoid receptor blocker. In another protocol, AB-4mice were fed a high-salt diet (AB-H) for 4 additional weeks. At 4 weeks, %FS was decreased and sympathetic activity was increased in AB-H compared with Sham. Expression of mineralocorticoid receptors and AT1R in the brain was higher in AB-H than in Sham. ICV infusion of eplerenone in AB-H attenuated salt-induced sympathoexcitation and the decreased %FS. ICV infusion of eplerenone also decreased brain AT1R expression. CONCLUSIONS: These findings indicate that activation of brain alphaENaC and AT1R through mineralocorticoid receptors contributes to the acquisition of Na sensitivity to induce sympathoexcitation. Therefore, high salt intake accelerates sympathetic activation and LV systolic dysfunction in a pressure overload model.