A RADIO-BIOASSAY FOR CORTICOTROPHIN

Abstract

ABSTRACT The increased uptake of 32P by the adrenals of the two day-old White Leghorn cockerel after corticotrophin (ACTH) stimulation was used as the end-point for the bioassay. Early results indicated that 32P entered the blood and adrenals rapidly from a subcutaneous injection site and augmented 32P uptake of adrenals occurred after ACTH stimulation. The simultaneous injection of ACTH and 32P resulted in a rapid and sustained increase of 32P incorporation by the chick adrenal. There was a 72 % increase of 32P uptake one-half hour after ACTH stimulation; maximum incorporation, 81 %, occurred eight hours after stimulation with the hormone. The simultaneous injection of ACTH and 32P with an 8-hour corticotrophin stimulation of the adrenals and 32P uptake became the basis for the bioassay of this hormone. The log dose-response studies showed the adrenals were sensitive to a wide range of ACTH concentrations (2.5 to 40.0 mU). The precision of this log dose-response line had a λ of 0.4762. Pretreatment with ACTH was found to increase the sensitivity of these glands to further treatment with this hormone. Pretreatment increased the precision of this bioassay from a λ of 0.3283 to 0.1563.