Immunohistochemical examination of the paraadenomatous "normal" pituitary. An evaluation of prolactin cell hyperplasia.

Prolactin cell hyperplasia has been described to occur in the paraadenomatous normal pituitary gland surrounding prolactinomas. However, compression of the glandular lobules and secretory cells alters profoundly the histological configuration of this tissue. No changes resembling those that occur during pregnancy are found. Immunohistochemical staining and counting of prolactin-(PRL-)secreting and growth hormone-(GH-)secreting cells in the normal, paraadenomatous pituitary gland obtained during extirpation of 24 prolactinomas and 5 adenomas causing acromegaly demonstrated that GH-secreting cells predominated in all biopsies obtained from acromegalic patients. PRL-secreting cells were more frequent than GH-secreting cells in 14 of 24 biopsies of the normal tissue surrounding prolactinomas. A particular predominance of PRL-secreting cells was found in patients with postoperative residual hyperprolactinemia. Direct comparison of adjacent sections demonstrates three cell types: One reacts with both antibodies and the other two react only with one or the other. We suggest that these groups are not stable but that cells belonging to one group can be transformed into cells belonging to the two other groups. Such a process, induced by extrahypophyseal factors, may explain the shift of relative cell frequency observed in the normal pituitary gland surrounding prolactinomas.