Antidiuretic Hormone (ADH), Vasopressin

ENDOCRINOLOGY, Hospital A/P, Adults, Pharmacy and Therapeutics

What ADH Does

ADH or Vasopressin is a hormone made in the hypothalamus, stored in the pituitary gland, and released by the posterior pituitary. It does two things:
1) Constricts small blood vessels and raises blood pressure and
2) Increases the absorption of water by the kidney. By making the kidneys reabsorb water, it limits urine output and helps control the body’s water balance. The two names of this hormone describe it’s two main functions. Antidiuretic hormone and Vasopressin.

ADH is the principal hormone that regulates sodium concentration in the body. It does so by controlling passive water reabsorption in the kidneys.

Aldosterone is the principal hormone that regulates the total body sodium (and thus volume since water follows sodium).

ADH is released by the posterior pituitary in response to sensors that detect an increase in blood osmolality (hyperosmolality) or decrease in blood volume (decrease in effective arterial volume). ADH may also be secreted when there is a decrease in blood pressure. Secretion of ADH may also be stimulated by angiotensin II

How ADH Works

ADH works in two ways:
1) Arteries: In the arterial blood vessels, it causes the smooth muscles to constrict. I.e. it causes vasoconstriction. That’s why we use ADH to treat shock!
2) Kidneys: In the kidneys, it inserts aquaporin-2 channels in the collecting ducts leading to passive water reabsorption.

ADH Surrogate / Indirect Assay

“Urine Osmolality is an indirect functional assay of the ADH-renal axis. Urine Osmolality range: 50 mOsm/L (no ADH) to 1200 mOsm/L (maximum ADH).” Pocket Medicine

Urine osmolality is a surrogate for ADH. A urine osmolality > 100 mOsm/L in a euvolemic patient without any other issues is suggestive of SIADH.

** Antidiuretic hormone = Vasopressin (arginine vasopressin)= a vasopressor

ADH doesn’t affect total body sodium like aldosterone does.

Disorders of ADH

  1. Diabetes insipidus (too little ADH or ADH doesn’t work). 
  2. SIADH (Syndrome of inappropriate ADH) – Too much ADH.
  3. Hyponatremia is almost always due to increased ADH.

 

References/ Resources

Int J Biochem Cell Biol. 2003 Nov;35(11):1495-9. https://www.ncbi.nlm.nih.gov/pubmed/12824060

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