Immunoreactive corticotrophin levels in adrenocortical insufficiency

Plasma concentrations of immunoreactive corticotrophin (ACTH) have been determined in 14 patients with untreated Addison's disease and in 42 patients with secondary adrenocortical insufficiency. Basal morning plasma ACTH levels were markedly raised in those with Addison's disease but were either in the normal range or undetectable in the group with secondary adrenocortical insufficiency. In the group with Addison's disease circulating ACTH values showed a definite nyctohemeral rhythm, a pronounced rise in response to insulin-induced hypoglycaemia, and an immediate fall following the intravenous injection of corticosteroids, with a half-life of between 13.5 and 44.2 minutes. When assays were performed with antisera directed against the portion of the ACTH molecule responsible for corticosteroidogenesis (the N-terminal portion) the apparent ACTH concentrations were lower than with antisera directed against the non-steroidogenic (C-terminal) portion of the molecule. This emphasizes that different antisera may give different apparent hormone concentrations, and that the ranges of values obtained in normal and abnormal states must be established for each antiserum.