Effect of thyroid function on the secretion of ACTH and cortisol

Patients with thyrotoxicosis were found to have a normal circadian rhythm of ACTH and F, but the level of serum F was lower than controls due to excessive degration and plasmal ACTH higher than controls by feedback regulation. The responsiveness of ACTH to dexamethasone suppression or insulin hypoglycemic stimulation was normal. Whereas the circadian secretion of ACTH and F was also normal in patients with primary hypotyroidism, the concentration of F was increased with normal ACTH level. There were stunted responses of ACTH to suppressing and stimulating tests. It was thought that the corticotrophs were insulted by hypertrophy or hyperplasia of thyrotrophs during primary hypothyroidism.