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.