Principle
ACTH stimulates the adrenal cortex to secrete corticosteroids (cortisol in humans).
Bioassay measures either adrenal gland weight, plasma corticosteroid levels, or specific physiological changes caused by elevated corticosteroids.
Methods of ACTH
Adrenal Ascorbic Acid Depletion Method (Older Method)
Rationale: ACTH causes the adrenal glands to use up ascorbic acid when synthesizing steroids.
Procedure:
Treat groups of rats with varying doses of standard ACTH and test ACTH.
After a specific time, sacrifice the animals and measure the remaining ascorbic acid in the adrenal glands.
Potency Determination: Plot the depletion of ascorbic acid vs. dose for standard and test.
Plasma Corticosterone Method
Procedure:
Inject standard or test ACTH into rats.
After a set period, measure plasma corticosterone levels.
Potency Determination: Compare the corticosterone response to standard vs. test across a range of doses.