BIOASSAY OF ADRENOCORTICOTROPIC HORMONE1

Abstract

Two methods are proposed for standardization of adrenocorticotrophic hormone. Both tests utilize the adrenal response of hypophysectomized rate, one being based on reparative changes in the atrophic adrenal when injn. of the hormone is begun after a postoperative interval, the other on maintenance of the adrenal when injn. is begun immediately post-operative. The unit based on repair of the adrenal is defined as the total dose in mg. necessary to cause beginning adrenal repair (redistribution of cortical lipid, and narrowing of subglomerular lipid-free zone) in [female] rats 26-28 days old at hypophysectomy and 14 days postoperative at the beginning of the 4-day injn. period. Based on this definition, the potency of pure sheep adrenocorticotrophic hormone is 100 unite per mg. In the test based on adrenal maintenance, the unit is defined as the daily dose in mg. necessary to maintain the pre-operative adrenal wt. for 15 days, in [male] rats hypophysectomized at 40 days of age. The pure hormone contains approx. 5 such units per mg. In both units, single daily intraperit. injns. were given, though greater biol. effects could be secured from a given amt. of hormone by administration in multiple daily injns. Both tests have been utilized in the chemical separation of adrenocorticotrophic hormone and are found equally dependable. The test based on adrenal repair requires less time and smaller quantities of hormone; the maintenance test, though requiring a longer injn. period, and a greater total amt. of hormone, has the advantage that it does not require microscopic examination, as it is based on measurement of adrenal wts.