Localization of inhibin/activin subunits in normal pituitary and in pituitary adenomas

The localization of inhibin/activin (I/A) subunits was investigated in human normal adenohypophysial cells and in 87 pituitary adenomas of different types, using immunohistochemistry. Monoclonal antibodies directed against α, βA and βB subunits of I/A were employed. In normal pituitary, α subunit of inhibin was detected only in FSH-positive gonadotrophs, while βA subunit of I/A was expressed in FSH-positive gonadotrophs, GH-cells and in a few PRL-cells. βB subunit was found in FSH-positive gonadotrophs, TSH-cells and a few LH-positive gonadotrophs. The three subunits of I/A were detected in the majority of nonfunctioning tumors, while functioning adenomas showed a significantly lower expression. This study shows that α, βA and βB subunits of I/A are expressed by specific adenohypophysial cell types and that they are characteristically present in nonfunctioning adenomas. These results suggest that inhibins and activins may play a role in the local regulation of pituitary hormonal secretion both in normal adenohypophysial cells and in pituitary adenomas.