Aldosterone is a steroid hormone, "the main mineralocorticoid hormone", produced by the outer section (zona glomerulosa) of the adrenal cortex in the adrenal gland. It plays a central role in the regulation of the plasma sodium (Na+), the extracellular potassium (K+) and arterial blood pressure. It does so mainly by acting on the distal tubules and collecting ducts of the nephron, increasing reabsorption and excretion of ions out of and into the tubular fluids of the kidney, to cause the conservation of sodium, secretion of potassium, and thereby indirectly influencing water retention or loss, and influencing blood pressure and blood volume. When dysregulated, aldosterone is pathogenic and contributes to the development and progression of cardiovascular and renal disease. Aldosterone has exactly the opposite function of the atrial natriuretic hormone secreted by the heart. Aldosterone is part of the renin–angiotensin system. It has a plasma half-life of under 20 minutes. Drugs that interfere with the secretion or action of aldosterone are in use as antihypertensives, like lisinopril, which lowers blood pressure by blocking the angiotensin-converting enzyme (ACE), leading to lower aldosterone secretion. The net effect of these drugs is to reduce sodium and water retention but increase retention of potassium. Another example is spironolactone, a potassium-sparing diuretic of the steroidal spirolactone group, which decreases blood pressure by releasing fluid from the body while retaining potassium. Aldosterone was first isolated by Simpson and Tait in 1953.

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