Effect of Aldosterone and MR Blockade on the Brain and the Kidney

The renin-angiotensin-aldosterone system (RAAS) plays a central role in the development of hypertension and the progression of end-organ damage. Although angiotensin-I converting enzyme (ACE) inhibitors and angiotensin II (Ang II) subtype-1 (AT₁) receptor antagonists can initially suppress plasma aldosterone, it is now well established that aldosterone escape may occur whereby aldosterone levels return to, or exceed, baseline levels. The classical effects of aldosterone relate mainly to its action on epithelial cells to regulate water and electrolyte balance. However, the presence of mineralocorticoid receptors (MR) at nonepithelial sites in the brain, heart and vasculature, is consonant with the fact that aldosterone also has direct effects in these tissues. Substantial evidence now exists that supports the action of aldosterone at non-epithelial sites which in turn provokes a number of deleterious effects on the cardiovascular system including necrosis and fibrosis of the vasculature and the heart, vascular stiffening and injury, reduced fibrinolysis, endothelial dysfunction, catecholamine release and production of cardiac arrhythmias. Several studies have now shown that vascular and target-organ protective effects of MR antagonism occurs in the absence of significant blood pressure lowering or fluid loss, which is consistent with a major role for endogenous mineralocorticoids as direct mediators of cardiovascular injury. Adverse cardiovascular effects may occur in response to aldosterone alone, activation of the RAAS or aldosterone escape during chronic ACE inhibition or AT₁ receptor antagonism. The specific blockade of aldosterone action should prove to be of great therapeutic value in the prevention of cerebral and renal vascular disease and associated end-organ damage.