What is the function of aldosterone?

Function of Aldosterone

Aldosterone is a steroid hormone that primarily regulates sodium and potassium balance in the body by promoting sodium reabsorption and potassium excretion in the kidneys, which directly affects blood pressure and fluid-electrolyte homeostasis. 1

Primary Physiological Actions

Aldosterone exerts its effects through several key mechanisms:

1. Renal Actions:

   • Binds to mineralocorticoid receptors in the distal convoluted renal tubule 2
   • Increases sodium reabsorption and water retention 2
   • Promotes potassium excretion 2
   • Maintains blood volume and blood pressure 1

2. Cardiovascular System Regulation:

   • Acts as a crucial regulator of blood pressure 1
   • Contributes to cardiovascular and kidney development 1
   • Modulates maternal-fetal health through the placental interface 1

Mechanism of Action

Aldosterone works through a specific receptor-mediated pathway:

• Binds competitively to mineralocorticoid receptors in the distal convoluted renal tubule 2
• Acts as a specific pharmacologic antagonist when blocked by medications like spironolactone 2
• Selectively binds to human mineralocorticoid receptors (as seen with eplerenone) 3
• Causes increased sodium and water retention while potassium is excreted 2

Clinical Significance

Normal Physiological Role

• In healthy individuals, aldosterone helps maintain fluid and electrolyte balance
• During pregnancy, elevated aldosterone contributes to physiological cardiovascular changes 1
• Increased angiotensinogen production and plasma renin activity lead to increased angiotensin I concentrations, favoring augmented angiotensin II production 1

Pathological States

1. Primary Aldosteronism:

   • Characterized by inappropriately high aldosterone production relative to sodium status 1
   • Cannot be suppressed with sodium loading 1
   • Causes hypertension, cardiovascular and kidney damage 1
   • Leads to sodium retention and increased potassium excretion 1
   • May present with hypertension, weakness, and hypokalemia 1

2. Screening and Diagnosis:

   • Plasma aldosterone-to-renin ratio is recommended for screening 1
   • In primary aldosteronism, patients have elevated plasma levels of aldosterone and low levels of renin activity 1
   • Electrolytes should be measured as excessive aldosterone causes sodium retention and potassium excretion 1

Treatment Approaches for Aldosterone Excess

When aldosterone levels are pathologically elevated:

• Pharmacological Management:

  • Spironolactone and eplerenone act as specific antagonists of aldosterone 2, 3
  • These medications block the binding of aldosterone to receptors 2, 3
  • Particularly useful in primary aldosteronism due to bilateral adrenal hyperplasia 1

• Surgical Management:

  • Laparoscopic adrenalectomy is recommended for aldosterone-producing adenomas 1
  • Open adrenalectomy is recommended when malignant hyperaldosteronism is suspected 1

Clinical Pearls and Pitfalls

• Important Caveat: While high aldosterone levels are typically pathological in conditions like primary aldosteronism, very high levels in response to chronic sodium deficiency can be homeostatic and protective of cardiovascular function 4

• Diagnostic Challenge: Hypokalemia, though classically associated with primary aldosteronism, is absent in the majority of cases and has a low negative predictive value 1

• Emerging Concept: Primary aldosteronism may exist on a spectrum of aldosterone excess states, with aldosterone excess potentially playing a role even in primary hypertension 1