IT HAS been clear for some time that the secretion of adrenocorticotropic hormone (ACTH) and β-lipotropin (β-LPH) appear to be linked, both being present in high concentrations in patients with disorders of hypersecretion (Cushing's syndrome, Addison's disease) and low in patients with disorders of hyposecretion (secondary adrenal insufficiency). Other molecular species also appear to be associated with ACTH secretion; for example, molecules larger than ACTH but with ACTH immunoreactivity have been found in many cases of "ectopic" ACTH secretion. Recent studies into the biosynthesis of ACTH and β-LPH appear to explain these interrelationships and hold forth the promise of important advances in our understanding of the relationship between the hypothalamus, pituitary, and the adrenal gland in man.
Early chemical studies have recognized the existence of several peptides that are structurally related to ACTH in the pituitary gland of many species including man. These include β-LPH, α-melanocyte-stimulating hormone (MSH), and β-MSH.