Immunohistochemical, electron microscopic, and morphometric studies of human prolactinomas after short-term bromocriptine treatment.

Two cases of human prolactinomas after short-term treatment with bromocriptine were studied by means of immunohistochemistry for prolactin, electron microscopy, and morphometry at the ultrastructural level. The results obtained showed an abundance of immunoreactive secretory granules in the tumor cells, a paucity in the electron microscopic images suggesting exocytosis of secretory granules, and no significant changes in the volume density of rough endoplasmic reticulum when compared with untreated (control) tumor cells. These findings strongly suggest that the effects of short-term bromocriptine treatment for lowering serum prolactin levels did not inhibit protein and secretory granule synthesis but rather caused a disturbance in the secretion of prolactin granules. The present morphometrical data suggest the possibility that a reduction in the number of cytoplasmic microtubules might be related to the disturbance of prolactin secretion.