Aldosterone – Hormone, Function and Medical Role
Aldosterone is a vital hormone produced by the adrenal cortex that regulates the balance of salt and water in the body, as well as blood pressure.
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Aldosterone is a vital hormone produced by the adrenal cortex that regulates the balance of salt and water in the body, as well as blood pressure.
What is Aldosterone?
Aldosterone is a steroid hormone produced in the zona glomerulosa of the adrenal cortex. It belongs to the group of mineralocorticoids and plays a central role in regulating electrolyte balance, blood volume, and blood pressure. Aldosterone acts primarily on the kidneys, where it controls the reabsorption of sodium and the excretion of potassium.
Mechanism of Action
Aldosterone binds to specific mineralocorticoid receptors in the cells of the renal tubules. This enhances the activity of sodium channels and sodium-potassium ATPases, resulting in the following effects:
- Increased reabsorption of sodium from the primary urine back into the bloodstream
- Increased excretion of potassium through the urine
- Increased water reabsorption, which raises blood volume and blood pressure
- Regulation of acid-base balance through effects on hydrogen ion excretion
Regulation of Aldosterone Secretion
The release of aldosterone is primarily controlled by the Renin-Angiotensin-Aldosterone System (RAAS). When blood pressure or blood volume drops, the kidneys release the enzyme renin. Renin cleaves angiotensinogen into angiotensin I, which is then converted by the angiotensin-converting enzyme (ACE) into angiotensin II. Angiotensin II stimulates the adrenal cortex to release aldosterone. Additional regulators include:
- Elevated blood potassium levels (directly stimulate aldosterone release)
- Adrenocorticotropic hormone (ACTH) from the pituitary gland (minor influence)
- Atrial natriuretic peptide (ANP), which inhibits aldosterone release
Medical Significance
Hyperaldosteronism
Excessive production of aldosterone is referred to as hyperaldosteronism. The primary form (Conn syndrome) is often caused by a benign adenoma of the adrenal cortex. Typical consequences include high blood pressure, low potassium levels (hypokalemia), and elevated sodium levels (hypernatremia). Secondary hyperaldosteronism occurs as a response to reduced renal blood flow or decreased blood volume.
Hypoaldosteronism
A deficiency of aldosterone, known as hypoaldosteronism, can occur in the context of Addison disease (primary adrenal insufficiency). Consequences include low sodium levels, elevated potassium levels, and a drop in blood pressure, which in severe cases can lead to a life-threatening Addisonian crisis.
Diagnosis
The following tests are used to assess aldosterone status:
- Measurement of aldosterone levels in blood or urine
- Determination of the aldosterone-to-renin ratio (ARR) to distinguish between primary and secondary hyperaldosteronism
- Imaging techniques such as CT or MRI of the adrenal glands when an adenoma is suspected
- Adrenal vein sampling for lateralization if needed
Therapeutic Relevance
Aldosterone is an important pharmacological target. Aldosterone antagonists such as spironolactone and eplerenone block the mineralocorticoid receptor and are used in the treatment of:
- Heart failure
- High blood pressure (hypertension)
- Primary hyperaldosteronism
- Liver cirrhosis with ascites
ACE inhibitors and AT1 receptor blockers indirectly lower aldosterone levels by inhibiting the formation of angiotensin II.
References
- Herold, G. et al.: Internal Medicine. Self-published, Cologne, 2023.
- Funder, J. W. et al.: The Management of Primary Aldosteronism. In: Journal of Clinical Endocrinology and Metabolism, 101(5):1889-1916, 2016. DOI: 10.1210/jc.2015-4061.
- World Health Organization (WHO): Cardiovascular Diseases and Hormonal Disorders. WHO Technical Report, Geneva, 2022.
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