Blood Pressure Regulation in Nephrotic Syndrome: Compensatory Mechanisms

Nephrotic syndrome (NS) features massive proteinuria → hypoalbuminemia → ↓ plasma oncotic pressure → fluid shifts to interstitium (edema) → effective arterial blood volume (EABV) depletion.

Compensatory Neurohormonal Activation

1. RAAS: Renin release → angiotensin II → vasoconstriction, aldosterone → Na⁺/water retention → restores intravascular volume.
2. Sympathetic nervous system: Baroreceptor unloading → norepinephrine → vasoconstriction, renin release.
3. ADH (vasopressin): Non-osmotic release (from hypovolemia) → water retention.
4. Endothelin-1: Vasoconstriction, Na⁺ retention.

Counter-Regulatory Factors

• Atrial natriuretic peptide (ANP) / BNP: Released by atrial stretch (if volume overloaded) → vasodilation, natriuresis.
• Prostaglandins (PGE₂, PGI₂): Renal vasodilation, inhibit Na⁺ reabsorption.
• Nitric oxide: Endothelial vasodilation.

Clinical Paradox

Despite total body Na⁺/water excess (edema), the kidney perceives hypovolemia (underfilling) → avid Na⁺ retention → perpetuates edema. BP may be normal, low, or high depending on balance of vasoconstrictors vs. vasodilators and cardiac function.

Therapeutic Implication

• Diuretics (loop) + albumin (controversial) to decongest.
• ACEi/ARB: reduce proteinuria, modulate RAAS — but caution if true intravascular depletion.
• Treat underlying cause (minimal change, FSGS, membranous, secondary).

Volume status assessment (clinical + biomarkers) guides therapy — not BP alone.