[Pathological changes of prolactinomas treated with bromocriptine].

Abstract

In order to investigate the pathological changes of prolactinomas induced by the treatment with bromocriptine, 12 cases of prolactinoma were studied using immunocytology and electronmicroscopy. Eight cases were treated with bromocriptine, 5 mg/day, for a few days before surgery, while 4 cases were given for several months. 1) Cases of the short-term administration All of the adenomas except one appeared to be eosinophilic by H-E stain. Electronmicroscopically, abundant secretory granules, measuring 100-350 nm, were found throughout the cytoplasm, while exocytosis, frequently seen in the common type of prolactinomas, could not be observed. With immunostains, prolactin was diffusely positive in the cytoplasm of most adenoma cells, though the intensity of immunostaining for prolactin was relatively faint compared with that of normal prolactin cells or usual prolactinomas. Immunoreactive prolactin was demonstrated on accumulated secretory granules, while it was negative in the Golgi apparatus and rough endoplasmic reticulum (ER). 2) Cases of the long-term administration The tumors corresponded to chromophobe adenomas and the immunoperoxidase techniques revealed the absence of prolactin in the cytoplasm. Electronmicroscopically, secretory granules, measuring about 100 nm, were infrequent and lined up along the cell membrane. Marked shrinkage of the Golgi apparatus and ER was noted with various stages of degenerative changes in adenoma cells. In conclusion, bromocriptine not only inhibits the release of prolactin, but also suppresses the synthesis of it at the initial phase. With a long-term administration of bromocriptine, the cell organelles related to the hormone production, such as the Golgi apparatus and ER show gradual shrinkage under the prolonged tonic inhibition for prolactin release and synthesis. This might be the mechanism by which bromocriptine leads prolactinomas to the shrinkage.