Aldosterone

Aldosterone is the body's main mineralocorticoid, a steroid hormone named for its effect on minerals such as sodium and potassium. It is made from cholesterol in the zona glomerulosa, the outermost layer of the adrenal cortex. Two signals chiefly trigger its release: angiotensin II, produced by the renin–angiotensin–aldosterone system when blood pressure or volume falls, and a rise in the potassium level of the blood.

Its main targets are cells in the last stretches of the nephron, the distal tubule and collecting duct. There it binds a receptor inside the cell and switches on genes for sodium channels and sodium–potassium pumps, so more sodium returns to the blood and more potassium leaves in the urine. Water follows the retained sodium by osmosis, so blood volume and blood pressure rise. Because these effects rely on new proteins being made, they build over hours rather than seconds.

Too much aldosterone, as in primary aldosteronism, causes high blood pressure that may come with low potassium; too little, as in Addison's disease, can cause low blood pressure and high potassium. Drugs that block its receptor, such as spironolactone, are used in heart failure and some forms of hypertension.