Pituitary Tumors and Failure of Endocrine Target Organs

In recent years, major technical advances, particularly the development of radioimmunoassays for pituitary hormones and sella turcica polytomography, have led to earlier diagnosis of pituitary tumors and renewed interest in their pathophysiology. In most instances, the etiology of these tumors continues to elude us. To put into perspective those tumors that are thought to be induced by endocrine target organ insufficiency, one might conceptually divide functioning pituitary tumors into two groups: those that presumably arise due to abnormalities at the level of the pituitary or above, and those that are due to peripheral hormone deficiency. The great majority of pituitary adenomas autonomously secrete prolactin or, less frequently, growth hormone, contrary to past beliefs that most were functionless. It has been estimated that greater than 65% of all pituitary tumors are prolactin-producing.¹ In contrast to most other hormones of the anterior pituitary, whose secretion is governed by "negative feedback," prolactin