Production of alpha-subunit of glycoprotein hormones by pituitary somatotroph adenomas in vitro

Abstract

Somatotroph adenomas of the pituitary secrete growth hormone in excess and are associated with acromegaly. Morphologically, they can be separated into two entities, densely and sparsely granulated variants. It has been shown that a number of somatotroph adenomas produce alpha-subunit of glycoprotein hormones; however, it is not clear whether alpha-subunit production correlates with tumor cell morphology. We studied 32 surgically removed pituitary somatotroph adenomas in tissue culture to determine structure-function correlations of growth hormone and alpha-subunit production. All tumors were classified on the basis of detailed histological, immunocytochemical and electron-microscopic studies. Fifteen tumors were densely granulated and 17 were sparsely granulated. In addition to growth hormone, all 15 densely granulated tumors released alpha-subunit in vitro, whereas of the 17 sparsely granulated tumors only 4 released alpha-subunit; moreover, the mean baseline levels of alpha-subunit were significantly higher in densely granulated adenomas than in sparsely granulated adenomas. Parallel response of release of both hormones was found during stimulation with growth hormone-releasing hormone or thyrotropin-releasing hormone and during suppression with somatostatin or bromocriptine in densely granulated tumors. alpha-subunit response to stimulation or suppression could not be determined with significance in sparsely granulated tumors because of low basal levels. The results indicate that alpha-subunit production and release is characteristic of densely granulated somatotroph adenomas and that alpha-subunit is coregulated with growth hormone by adenohypophysiotropic substances; in contrast, alpha-subunit production, by sparsely granulated somatotroph adenomas is rare and, when present, much lower in quantity.(ABSTRACT TRUNCATED AT 250 WORDS)