Anterior pituitary corticotrophin cells secrete ACTH as part of a larger precursor molecule, pro-opiomelanocortin. Post-translational cleavage of this precursor yields three major peptides: ACTH, beta-LPH and N-POMC. Experiments both in vivo and in vitro suggest that N-POMC may act as a prohormone amplifier for ACTH-induced adrenal steroidogenesis and as regulator of adrenocortical cell growth. The secretion of POMC is under the control of CRF. These findings are discussed in relation to the pathophysiology of corticotrophinoma. The primary defect in this condition appears to reside at the level of the anterior pituitary cell and is readily amenable to treatment by trans-sphenoidal microsurgery. The estimation of plasma ACTH concentrations is proving useful in the monitoring of various clinical conditions including Addison's disease and congenital adrenal hyperplasia.
Acromegaly is a rare disease caused by a GH-secreting pituitary adenoma in more than 99% of patients. At diagnosis, about 75% of patients have macroadenomas. The mean age at diagnosis is about 45 years. Clinical features of acromegaly may be related to excess GH or IGF-1 or to associated mass effect including hypopituitarism, because most patients present with pituitary macroadenomas ( Box 2 and Fig. 4 ). Excess growth hormone before the fusion of the epiphyseal growth plates results in gigantism. Acromegalic patients probably carry an increased risk of malignancy such as premalignant adenomatous colon polyps and colon cancer, although published data vary greatly in their findings.