mineralocorticoid

A mineralocorticoid is the corticosteroid in charge of the body's salt and water balance. Think of it as the manager of the kidney's salt-recycling depot: it decides how much sodium to keep, how much potassium to throw away, and in doing so it strongly influences blood volume and blood pressure. The chief natural one is aldosterone.

Aldosterone, made in the adrenal cortex, acts on the mineralocorticoid receptor in kidney tubule cells. There it boosts reabsorption of sodium (and with it, water) back into the blood while promoting excretion of potassium and hydrogen ions into the urine. Like other steroid hormones it works as a nuclear receptor signal, altering gene expression to increase the channels and pumps that move these ions. Its release is driven mainly by the renin–angiotensin system and by high blood potassium.

In pharmacology, mineralocorticoid activity is something we both supply and block. The drug fludrocortisone provides mineralocorticoid replacement when the adrenal glands fail. Far more commonly, we block the receptor: drugs like spironolactone and eplerenone are mineralocorticoid receptor antagonists used as potassium-sparing diuretics and in heart failure and resistant hypertension. A practical caveat: blocking aldosterone can raise blood potassium dangerously, so potassium levels and kidney function are monitored.