Analysis of hormone secretion by clinically nonfunctioning human pituitary adenomas using the reverse hemolytic plaque assay.

The reverse hemolytic plaque assay was used to study hormone release in vitro by seven clinically nonfunctioning human pituitary adenomas associated with no clinical or biochemical evidence of hormone excess. Four of seven tumors were oncocytomas, one a null cell adenoma, and two gonadotroph adenomas based on immunocytochemical and ultrastructural features. In all seven tumors, plaques were formed with antiserum against beta FSH; four produced plaques for beta LH, and five for glycoprotein hormone alpha-subunit. The percentage of plaque-forming cells and the mean size of plaques were smaller than those of clinically functioning adenomas studied for comparison (five GH- and/or PRL-producing adenomas). These results correlated with those of hormone release in tissue culture, immunocytochemistry on paraffin secretions of the tumors, and immunocytochemistry after reverse hemolytic plaque assay. We conclude that clinically nonfunctioning pituitary adenomas release small quantities of hormones, primarily gonadotropins, and that hormone release is attributable to only a small percentage of tumor cells.