Aldosterone Is Essential for Angiotensin II-Induced Upregulation of Pendrin

The renin-angiotensin-aldosterone system has an important role in the control of fluid homeostasis and BP during volume depletion. Dietary salt restriction elevates circulating angiotensin II (AngII) and aldosterone levels, increasing levels of the Cl-/HCO3- exchanger pendrin in beta-intercalated cells and the Na+-Cl- cotransporter (NCC) in distal convoluted tubules. However, the independent roles of AngII and aldosterone in regulating these levels remain unclear. In C57BL/6J mice receiving a low-salt diet or AngII infusion, we evaluated the membrane protein abundance of pendrin andNCC; assessed the phosphorylation of the mineralocorticoid receptor, which selectively inhibits aldosterone binding in intercalated cells; and measured BP by radiotelemetry in pendrinknockout and wild-type mice. A low-salt diet or AngII infusion upregulated NCC and pendrin levels, decreased the phosphorylation of mineralocorticoid receptor in beta-intercalated cells, and increased plasma aldosterone levels. Notably, a low-salt diet did not alter BP in wild-type mice, but significantly decreased BP in pendrinknockout mice. To dissect the roles of AngII and aldosterone, we performed adrenalectomies inmice to remove aldosterone from the circulation. In adrenalectomized mice, AngII infusion again upregulated NCC expression, but did not affect pendrin expression despite the decreased phosphorylation of mineralocorticoid receptor. By contrast, AngII and aldosterone coadministration markedly elevated pendrin levels in adrenalectomized mice. Our results indicate that aldosterone is necessary for AngII-induced pendrin upregulation, and suggest that pendrin contributes to the maintenance of normal BP in cooperation with NCC during activation of the reninangiotensin- aldosterone system by dietary salt restriction.