Distribution of growth hormone and prolactin in secretory granules of the normal and neoplastic human adenohypophysis

Growth hormone [GH] and prolactin [PRL] can be demonstrated simultaneously in electron micrographs by means of the double immunocytochemical labeling technique using colloidal gold particles of two different sizes. This method was used to study biopsy specimens obtained from 15 patients suffering from acromegaly, 11 patients suffering from prolactinomas, and eight biopsy specimens obtained during adenomectomy from the normal, paraadenomatous pituitary tissue. Four granule populations with different immunoreactions were found: (1) granules containing GH only, (2) granules containing PRL only, (3) mixed granules containing GH and PRL, and (4) granules displaying no immunoreactivity. The existence of mixed granules indicated that the two hormones are synthesized by the same cell and in communicating compartments of the cells; i.e., the rough-surfaced endoplasmic reticulum. The number of GH-containing granules (pure GH granules and mixed GH-PRL granules) was greater than that of PRL-containing granules (pure PRL granules and mixed PRL-GH granules) in adenomas causing acromegaly and in the normal pituitary tissue, whereas the opposite was true for prolactinomas. The number of PRL-containing granules was larger in biopsy specimens from patients who had acromegaly and hyperprolactinemia than in patients with acromegaly and normal serum PRL levels.