Aldosterone as a determinant of cardiovascular and renal dysfunction.

Abstract

Aldosterone is a major regulator of extracellular fluid volume and the principal determinant of potassium metabolism 1,2,3,4,5. These effects are mediated by the binding of aldosterone to the mineralocorticoid receptor in target tissues, primarily the kidney. Volume is regulated through a direct effect on the collecting duct, where aldosterone promotes sodium retention and potassium excretion. The reabsorption of sodium ions produces a fall in the transmembrane potential, thus enhancing the flow of positive ions (such as potassium) out of the cell into the lumen. The reabsorbed sodium ions are transported out of the tubular epithellium into the renal interstitial fluid and from there into the renal capillary circulation. Three primary mechanisms control aldosterone release—the renin-angiotensin system, potassium, and adrenocorticotropic hormone. The renin-angiotensin system controls extracellular fluid volume via regulation of aldosterone secretion. In effect, the renin-angiotensin system keeps the circulating blood volume constant by causing aldosterone-induced sodium retention during volume deficiency and by decreasing aldosterone-dependent sodium retention when volume is ample. In recent years there has been a radical shift in our view of aldosterone's effects on the heart, the vasculature and the kidney6,7,8,9. Aldosterone's endocrine properties have taken on a broader perspective, involving non-classic actions in non-epithelial cells found in non-classic target tissues6, 10,11,12,13,14,15. The traditional concept, that aldosterone is synthesized only in the adrenal glomerulosa cell and acts almost exclusively on the kidney to modify sodium and potassium homoeostasis, needs to be expanded. There is increasing evidence that aldosterone can have an effect on vascular remodelling and collagen formation, and a non-genomic action to modify endothelial function. Among the most intriguing effects of aldosterone are its impact on fibrosis and activity associated with a cell surface receptor in certain target tissues, including endothelial cells 6, 7, 16,17,18,19. These actions contribute substantially to the pathophysiology of congestive heart failure (CHF), as well as progressive renal dysfunction. This new information has increased interest in the development of an antagonist to block aldosterone's effect, not just because of its diuretic action but primarily because of its potential cardiovascular and renal protective effects. In this review I consider the broad spectrum of non-genomic effects of aldosterone. It is becoming increasingly evident that these effects, occurring independently of haemodynamic factors, contribute to enhanced cardiovascular risk manifested by congestive heart failure and progressive renal disease. I also discuss the clinical trials with selective aldosterone receptor antagonists that are currently underway in patients with left ventricular hypertrophy, essential hypertension and systolic hypertension, and in those who have experienced myocardial infarction. Such trials will enhance our understanding of the role of aldosterone in the pathophysiology of cardiovascular disease. Also, selective aldosterone receptor antagonism holds promise for a reduction in cardiovascular and renal disease morbidity and mortality, and for enhancement of patient wellbeing.