Electron microscopy of human pituitary adenomas. Correlation of the secretory granules with the experimentally and clinically evaluated hormone synthesis function of the adenoma tissue.

Abstract

Ultrastructural features of the secretory granules of human pituitary adenomas obtained at operation from 18 patients were studied in correlation with the clinical features and abilities of the tumor tissue to synthesize and release growth hormone (HGH) and prolactin. These abilities were measured quantitatively, isolating the hormones with polyacrylamide gel disc electrophoresis after in vitro labelling of the hormones with 14C-leucine. The pituitary adenomas without recognizable functional significance (8 cases), which clinically manifested hypopituitarism, showed low hormone synthesis. In the cytoplasm, small secretory granules (100-200 nm in diameter) covered with a limiting membrane and having a clear halo and dense core were sparsely distributed. In prolactin producing adenomas, which clinically manifested hyperprolactinemia with galactorrheaamenorrhea syndrome (3 cases), higher prolactin synthesis was found. In the tumor cells, round and pleomorphic secretory granules were observed. The latter, measuring up to 450 nm in diameter, were considered to be prolactin granules. Round secretory granules measuring 150-350 nm in diameter were commonly observed in the adenomas showing high HGH synthesis function and/or elevated plasma HGH concentration. This type of granules were common in HGH producing adenomas clinically manifesting acromegaly (5 cases), and, therefore, were considered as HGH granules. Though less irregularly-shaped than in prolactin producing adenomas, pleomorphic secretory granules were also found in the HGH producing adenomas together with the round granules. The high prolactin synthesis and release functions of the HGH producing adenomas would be correlated to the presence of this type of granules. There were two tumors in which, the ultrastructural appearance could not be correlated with clinical features or measured abilities of the hormone synthesis and release.