Bioassay of Vasopressin (ADH)

Principle of Vasopressin

• Vasopressin (antidiuretic hormone, ADH) has two major effects:

• Antidiuretic effect (increases water reabsorption in the kidney).

• Vasopressor effect (vasoconstriction, increases blood pressure).

Methods

Antidiuretic (Rat Antidiuretic Assay)

Procedure:

• Deprive rats of water for a specific time so that they are sensitive to ADH.

• Inject the standard vasopressin and measure urine volume (or urine osmolality) for a given period.

• Repeat with the test preparation.

• Potency Determination: Compare the reduction in urine output (or increase in urine osmolality) for the standard vs. test.

Pressor (Blood Pressure) Assay

Procedure:

• Use an anesthetized rat or dog with an arterial blood pressure cannula.

• Administer standard vasopressin and measure the rise in mean arterial pressure.

• Wash out, then administer the test sample.

• Potency Determination: Compare the dose required to produce a specific increase in blood pressure (e.g., 20 mmHg) for both standard and test.