Sympathetic regulation of NCC in norepinephrine-evoked salt-sensitive hypertension in Sprague-Dawley rats

Salt sensitivity of blood pressure is characterized by inappropriate sympathoexcitation and renal Na + reabsorption during high salt intake. In salt-resistant animal models, exogenous norepinephrine (NE) infusion promotes salt-sensitive hypertension and prevents dietary Na + -evoked suppression of the Na + -Cl − cotransporter (NCC). Studies of the adrenergic signaling pathways that modulate NCC activity during NE infusion have yielded conflicting results implicating α 1 - and/or β-adrenoceptors and a downstream kinase network that phosphorylates and activates NCC, including with no lysine kinases (WNKs), STE20/SPS1-related proline-alanine-rich kinase (SPAK), and oxidative stress response 1 (OxSR1). In the present study, we used selective adrenoceptor antagonism in NE-infused male Sprague-Dawley rats to investigate the differential roles of α 1 - and β-adrenoceptors in sympathetically mediated NCC regulation. NE infusion evoked salt-sensitive hypertension and prevented dietary Na + -evoked suppression of NCC mRNA, protein expression, phosphorylation, and in vivo activity. Impaired NCC suppression during high salt intake in NE-infused rats was paralleled by impaired suppression of WNK1 and OxSR1 expression and SPAK/OxSR1 phosphorylation and a failure to increase WNK4 expression. Antagonism of α 1 -adrenoceptors before high salt intake or after the establishment of salt-sensitive hypertension restored dietary Na + -evoked suppression of NCC, resulted in downregulation of WNK4, SPAK, and OxSR1, and abolished the salt-sensitive component of hypertension. In contrast, β-adrenoceptor antagonism attenuated NE-evoked hypertension independently of dietary Na + intake and did not restore high salt-evoked suppression of NCC. These findings suggest that a selective, reversible, α 1 -adenoceptor-gated WNK/SPAK/OxSR1 NE-activated signaling pathway prevents dietary Na + -evoked NCC suppression, promoting the development and maintenance of salt-sensitive hypertension.