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.