Application of Cytochemical Bioassays of Adrenocorticotrophin

Abstract

The half-time in the circulation of biologically active corticotrophin endogenous to the subject was calculated from a study in which a male subject was given 100 mg of Cortisol intravenously and the levels of ACTH were measured at frequent intervals (Rees et al. 1973 b). The results showed that the Cortisol suppressed the secretion of ACTH, the levels falling from 43 pg/ml to 34 fg/ml (Fig. 9.1). This gave a half-time, over the first part of the graph, of 10.4 min. In other studies (Daly et al. 1974 a) where only 5 mg of Cortisol or 0.5 mg of dexamethasone were used to produce the suppression, the half-times were only about 7 min. It may be remarked that, because the assay is so sensitive, only very small samples of blood need to be taken so that it was perfectly feasible to remove the seven samples required for Fig. 9.1 without incommoding the subject.