Aldosterone is a 21-carbon steroid derived from precursor cholesterol. It is the main endogenous mineralocorticoid hormone. It is produced from the precursor corticosterone by the zona glomerulosa of the adrenal cortex mainly in response to angiotensin II.
Aldosterone probably causes activation of a specific Na+/K+ active pump in the distal renal tubule. This leads to reabsorption of sodium and water from the urine in exchange for potassium and hydrogen ions. Sodium retention causes a secondary retention of water.
Aldosterone causes a reduction in the sodium and an increase in the potassium concentration of both sweat and saliva. This effect is not seen in cystic fibrosis.
Regulation of aldosterone release is by:
- angiotensin II via the renin-angiotensin system
- potassium, via a direct action on the zona glomerulosa:
- low levels of serum potassium appear to have an inhibitory effect on aldosterone secretion
- high levels of serum potassium increase aldosterone secretion
- ACTH: minimal effect except at very high concentrations when it stimulates secretion
- hyponatraemia increases aldosterone secretion via a direct effect on the zona glomerulosa
Aldosterone may be competitively inhibited by drugs such as spironolactone.