THE THREE SUBTYPES OF PITUITARY ADRENOCORTICOTROPIN

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Abstract
CRUDE extracts cannot be medically useful until a satisfactory bioassay method permits their potency to be described in quantitative units which parallel the clinical potency in patients. Bioassay methods for corticotropin were unsatisfactory until the adrenal ascorbic acid depletion method was introduced by Sayers, Sayers, and Woodbury, in 1947.1 Using rats which had been hypophysectomized to remove their source of endogenous corticotropin, these investigators demonstrated a linear relationship between the logarithm of the dosage of intravenously administered corticotropin and the resulting decrease in adrenal ascorbic acid concentration. An acceptable assay permitted standards for corticotropin to be established. The first was the Armour "milligram," later superseded by the International Unit and the U. S. P. unit; all are essentially identical and interchangeable. Until quite recently, the clinical activity of intramuscularly administered corticotropins appeared to parallel potency determined by the ascorbic acid depletion bioassay, in which the corticotropins are administered intravenously.