noun, plural: aldosterones
A mineralocorticoid is a substance (a drug or a hormone) produced mainly in the adrenal cortex. It is involved in the regulation of electrolytes (e.g. ions) and water balance through acting on ion transport in the epithelial cells of the renal tubules. The primary example of mineralocorticoid is the aldosterone.
Aldosterone is produced naturally in the zona glomerulosa at the outer edge of the adrenal cortex. It is biosynthesized from cholesterol and makes use of aldosterone synthase (a steroid hydroxylase cytochrome P450 enzyme located in the zona glomerulosa). The biosynthesis of aldosterone is stimulated by the following factors: (1) increase in angiotensin III levels in the plasma, (2) increase in plasma angiotensin II, ACTH, or potassium levels, (3) plasma acidosis, (4) adrenoglomerulotropin (promotes aldosterone secretion), and (5) stretch receptors stimulating the release of aldosterone from the adrenal gland, particularly when blood pressure is decreased.
Aldosterone acts on the kidneys, particularly involved in the reabsorption of sodium as well as the passive reabsorption of water. It is also associated with lowering the plasma potassium concentration. It does so through the following mechanisms:1
- Aldosterone enters the principal cells of the distal tubule and the collecting duct of the kidney nephron and then acts on the nuclear mineralocorticoid receptor. This leads to the activation of the basolateral Na+/K+ pumps to pump out 3 Na+ ions out of the cell into the interstitial fluid. Concurrently, 2 K+ ions are taken into the cell from the interstitial fluid. As a result, a concentration gradient causes Na+ ions and water to be reabsorbed into the blood while K+ ions are secreted into the urine from the lumen of collecting duct.
- Aldosterone upregulates the epithelial sodium channels in the collecting duct and the colon. This increases the permeability of Na+ ions in the apical membrane
- Aldosterone stimulates K+ secretion into the tubular lumen
- Aldosterone stimulates Na+ and water reabsorption in exchange for K+ in the gut, salivary glands, and sweat glands
- Aldosterone stimulates H+ secretion via the H+/ATPase in the intercalated cells of the cortical collecting tubules
With these biological actions of aldosterone, it is associated in the increase of blood pressure and blood volume. In high levels though, it causes sodium retention, high blood pressure, heart rhythm irregularities, and possibly paralysis. The condition wherein there is an abnormally high aldosterone level is referred to as hyperaldosteronism whereas the condition in which the level of aldosterone is abnormally decreased is called hypoaldosteronism.
1 Aldosterone. Wikipedia.org. Retrieved from []