Ménage à trois: Aldosterone, sodium and nitric oxide in vascular endothelium

Aldosterone, a mineralocorticoid hormone mainly synthesized in the adrenal cortex, has been recognized to be a regulator of cell mechanics. Recent data from a number of laboratories implicate that, besides kidney, the cardiovascular system is an important target for aldosterone. In the endothelium, it promotes the expression of epithelial sodium channels (ENaC) and modifies the morphology of cells in terms of mechanical stiffness, surface area and volume. Additionally, it renders the cells highly sensitive to small changes in extracellular sodium and potassium. In this context, the time course of aldosterone action is pivotal. In the fast (seconds to minutes), non-genomic signalling pathway vascular endothelial cells respond to aldosterone with transient swelling, softening and insertion of ENaC in the apical plasma membrane. In parallel, nitric oxide (NO) is released from the cells. In the long-term (hours), aldosterone has opposite effects: The mechanical stiffness increases, the cells shrink and NO production decreases. This leads to the conclusion that both the physiology and pathophysiology of aldosterone action in the vascular endothelium are closely related. Aldosterone, at concentrations in the physiological range and over limited time periods can stabilize blood pressure and regulate tissue perfusion while chronically high concentrations of this hormone over extended time periods impair sodium homeostasis promoting endothelial dysfunction and the development of tissue fibrosis.