Plasma immunoreactive corticotrophin and lipotrophin in Cushing's syndrome and Addison's disease.

Plasma immunoreactive corticotrophin (ACTH) and lipotrophin (LPH) were measured in patients with raised circulating concentrations from a pituitary or an ectopic source. They were measured again in seven patients after they had received hydrocortisone. Plasma ACTH concentrations were higher than LPH concentrations in patients with a pituitary source of their hormones, whereas this relation was reversed when the source was ectopic. After hydrocortisone administration the half life of immunoreactive ACTH was 40 minutes and that of LPH 95 minutes, resulting in a reversal of the normal relation of ACTH to LPH. The use of two antisera with different specificities for measuring LPH has further shown that pituitary LPH differs from ectopic LPH. Relatively less gamma-LPH than beta-LPH was produced from ectopic sources, the relation being reversed in patients with a pituitary source for their raised concentrations. Measuring plasma LPH as well as ACTH might therefore help in deciding whether a patient with Cushing's syndrome has a pituitary or ectopic source of ACTH, which sometimes presents a difficult clinical problem.