Abstract 11005: Activation of Hypothalamic Mineralocorticoid Receptor-Independent Epithelial Sodium Channels Leads to Salt-Sensitive Hypertension in Mouse Model of Metabolic Syndrome

Abstract

Introduction and Hypothesis: Metabolic syndrome (MetS) is often associated with salt-sensitive hypertension. In genetic salt-sensitive hypertensive models, activation of the hypothalamic mineralocorticoid receptor (MR)-epithelial sodium channel (ENaC) pathway has been established as a major worsening factor. However, in MetS, contribution of the hypothalamic MR-ENaC pathway to salt-sensitive hypertension remains unknown. Therefore, we determined whether the hypothalamic MR-ENaC pathway activation leads to salt-sensitive hypertension in MetS. Methods and Results: Diet-induced obesity (DIO) was achieved in male C57BL/6 mice by feeding them a high-fat diet from 4 weeks of age. Mice fed a normal diet served as controls (CON). Mice at 12 weeks of age were given tap water with regular salt (RS) or 1% NaCl (high salt; HS) for 8 weeks. HS led to increased systolic blood pressure only in DIO-mice, and not in CON-mice (DIO-HS: 122±3 mmHg vs DIO-RS: 107±2 mmHg, CON-HS: 109±2 mmHg vs CON-RS: 105±1 mmHg, n=6/group, p<0.05). In DIO-mice, 24-h urinary norepinephrine excretion after salt loading was significantly higher than that before salt loading (244±18 ng/day vs 371±29 ng/day, n=6 in each, p<0.05). HS-induced hypertension was significantly prevented by intracerebroventricular infusion of the ENaC blocker benzamil (Ben), but not the MR blocker spironolactone (Spl; DIO-HS-Vehicle 122±1 mmHg, DIO-HS-Ben 108±1 mmHg, DIO-HS-Spl 119±1 mmHg, n=6 in each, p<0.05). Expression of hypothalamic serum and glucocorticoid-regulated kinase (SGK) 1, a marker of MR activity, did not differ between in CON-mice and DIO-mice. However, the SGK1 phosphorylation level was greater in DIO-mice than in CON-mice, suggesting MR-independent SGK1 activation. Water intake and urinary sodium excretion did not differ between in DIO-HS-Vehicle and DIO-HS-Ben. Interestingly, salt loading-induced plasma arginine vasopressin (AVP) secretion was significantly prevented in DIO-HS-Ben. Conclusions: These findings suggest that salt-induced hypertension in DIO-mice results from MR-independent hypothalamic SGK1-ENaC activation with systemic AVP secretion. Hypothalamic ENaC could be a novel therapeutic target in salt-induced hypertension of MetS.