Human pituitary somatotroph adenoma and prolactinoma: an ultrastructural and immunoelectron microscopical study.

17 cases of pituitary somatotroph adenoma and 38 cases of prolactinoma were studied with electron microscopy and immunoelectron microscopy using protein A-gold complex. 4 adenomas were shown by immunoelectron microscopy to contain simultaneously growth hormone (GH)-producing and prolactin (PRL)-producing cells. 6 cases were classified as densely granulated GH adenomas and 11 as sparsely granulated variant, whereas only 3 adenomas out of 38 prolactinomas were identified as densely granulated adenomas. The present study showed that not all cells with fibrous bodies possessed secretory granules positive for GH, and in some cells with fibrous bodies PRL-producing granules were also detected. Misplaced exocytosis was found frequently in the sparsely granulated prolactinomas. From these findings it may be suggested that fibrous bodies are not a morphological feature characteristic of pituitary somatotroph adenomas.