Bioassay of Vasopressin (ADH)

• Bioassay of Vasopressin (ADH): Commonly done using rat pressor or antidiuretic assays.
•  Bioassay of Vasopressin (ADH): Measures vasoconstriction or urine volume reduction in test animals.

Principle Bioassay of Vasopressin (ADH)

• Vasopressin (antidiuretic hormone, ADH) has two major effects:
  1. Antidiuretic effect (increases water reabsorption in the kidney).
  2. Vasopressor effect (vasoconstriction, increases blood pressure).

Methods

1. Antidiuretic (Rat Antidiuretic Assay)

• Procedure:
  1. Deprive rats of water for a specific time so that they are sensitive to ADH.
  2. Inject the standard vasopressin and measure urine volume (or urine osmolality) for a given period.
  3. Repeat with the test preparation.
• Potency Determination: Compare the reduction in urine output (or increase in urine osmolality) for the standard vs. test.

2. Pressor (Blood Pressure) Assay

• Procedure:
  1. Use an anesthetized rat or dog with an arterial blood pressure cannula.
  2. Administer standard vasopressin and measure the rise in mean arterial pressure.
  3. 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.

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