What is vasopressin, also known as antidiuretic hormone (ADH)?

Vasopressin: A Multifunctional Hormone with Antidiuretic and Vasoconstrictive Properties

Vasopressin is a peptide hormone that functions primarily as an antidiuretic hormone (ADH) regulating water balance and as a vasoconstrictor acting on blood vessels through different receptor subtypes. 1

Biochemical Structure and Production

• Vasopressin is a nonapeptide (nine amino acid peptide) synthesized in the hypothalamus and released from the posterior pituitary gland
• Chemical structure: Cyclo (1-6) L-Cysteinyl-L-Tyrosyl-L-Phenylalanyl-L-Glutaminyl-L-Asparaginyl-L-Cysteinyl-L-Prolyl-L-Arginyl-L-Glycinamide 2
• Molecular formula: C46H65N15O12S2 with a molecular weight of 1084.23 2
• Also known as arginine vasopressin (AVP) or antidiuretic hormone (ADH) 3, 1

Physiological Roles and Receptor Types

Vasopressin exerts its effects through three main receptor subtypes:

V1 Receptors (V1a and V1b)

• V1a receptors: Located primarily on vascular smooth muscle cells and in the myocardium
  • Mediate vasoconstriction effects
  • Coupled to phospholipase C, resulting in calcium release and subsequent vasoconstriction 1, 2
• V1b receptors: Found in the central nervous system
  • Involved in mood and behavior modulation 4

V2 Receptors

• Located predominantly in the kidney collecting ducts and medullary tubules
• Mediate the antidiuretic effects of vasopressin
• Coupled to adenyl cyclase, leading to:
  • Increased water permeability in collecting ducts
  • Insertion of aquaporin-2 (AQP2) water channels into the luminal membrane
  • Enhanced water reabsorption and concentrated urine production 1, 2

Clinical Applications

1. Treatment of Vasodilatory Shock

• Vasopressin (0.01-0.04 units/min) is recommended for septic shock and other types of vasodilatory shock 1, 5
• Acts through V1 receptors to increase systemic vascular resistance and mean arterial blood pressure
• Reduces the dose requirements for norepinephrine in patients with sepsis 2
• Caution: Doses above 0.04 U/min may lead to cardiac arrest 6

2. Management of Diabetes Insipidus

• Desmopressin (synthetic vasopressin analog) is used as replacement therapy for central diabetes insipidus 1
• Addresses polyuria and polydipsia by restoring water reabsorption in the kidneys

3. Treatment of Hyponatremia in SIADH

• V2 receptor antagonists (e.g., tolvaptan) are used to treat hyponatremia associated with Syndrome of Inappropriate ADH (SIADH) 3, 1
• SIADH occurs in approximately 1-5% of lung cancer patients, particularly small cell lung cancer 3

4. Cardiopulmonary Resuscitation

• A 40-U bolus dose may be considered during cardiopulmonary resuscitation to replace the first or second bolus of epinephrine 5

Pharmacokinetics

• Rapid onset of action with peak effect within 15 minutes
• Short half-life (≤10 minutes) at clinical infusion rates
• Predominantly metabolized by liver and kidney, with only about 6% excreted unchanged in urine 2
• Clearance increases significantly during pregnancy due to placental vasopressinase 2

Side Effects and Precautions

• Potential side effects include ischemic skin lesions and intestinal ischemia 6
• Overdosage can lead to water retention and hyponatremia 1
• Contraindicated in moderate to severe renal impairment (creatinine clearance <50 mL/min) 1
• Drug interactions with indomethacin, tetra-ethylammonium, and furosemide can alter vasopressin's effects 2

Vasopressin represents a critical hormone in maintaining physiological homeostasis through its dual roles in water regulation and vascular tone control, with important clinical applications in shock management, water balance disorders, and resuscitation efforts.