Aldosterone

Aldosterone is a mineralocorticoid secreted by the adrenal cortex. The release of aldosterone is controlled primarily by the renin-angiotensin-aldosterone system. A decrease in extracellular fluid results in decreased blood flow through the kidneys, which in turn stimulates production and secretion of renin by the kidneys. Renin acts on angiotensinogen to form Angiotensin I which, in the presence of angiotensinconverting enzyme (ACE), is converted to Angiotensin II. Angiotensin II stimulates the adrenal cortex to increase aldosterone production. The effects of aldosterone occur in the renal distal tubule, where it causes increased reabsorption of sodium and chloride and increased excretion of potassium and hydrogen ions. The result of these actions is retention of increased water and an increase in extracellular fluid. The ultimate effect of changes in aldosterone level is regulation of blood pressure.
Measurement of aldosterone level is performed on both the plasma and the urine. This information assists in the diagnosis of primary aldosteronism, caused by an abnormality of the adrenal cortex, and of secondary aldosteronism, which may result from overstimulation of the adrenal cortex by a substance such as angiotensin or ACTH.