Growth hormone-releasing activity in extracts of bronchial carcinoid and pancreatic islet tumors associated with acromegaly

Data presented provide evidence for the production of a GHRF by carcinoid and pancreatic islet tumors which stimulates GH overproduction by the pituitary leading to acromegaly and to pituitary tumor formation. These features, which constitute an 'ectopic GHRF syndrome', provide an explanation for the association of pituitary tumors with carcinoid and pancreatic islet tumors of the multiple endocrine neoplasia syndrome, Type I, and indicate that consideration of an extrapituitary tumor is warranted in every patient with acromegaly. These tumors produce both GHRF and somatostatin and the ultimate clinical expression undoubtedly reflects the ratio of release of these two factors into circulation. The identity of the GHRF in various tumors remains to be established as does the relationship by hypothalamic GHRF. However, the results indicate that excess secretion of GHRF can produce not only enhanced GH secretion but can also lead to pituitary tumor formation, and, therefore, provide evidence to support the hypothesis that at least some GH-secreting pituitary tumors are caused by hypersecretion of a hypothalamic GHRF.