Lysosomal disposal of secretory granules and their transformation into pigment particles in spontaneous prolactin cell adenomas of the rat pituitary.

Light and electron microscopic study of spontaneous prolactin cell adenomas, found at autopsy of 26 aging female Long-Evans rats and of 9 aging male Wistar rats, revealed pigment particles in the cytoplasm of some adenoma cells. It is postulated that most of the pigment particles derive from secretory granules. The presence of crinophagy and autophagy are interpreted as the morphologic expressions of lysosomal activation. The causative mechanisms accounting for lysosomal disposal of secretory granules and their transformation to pigment particles remain to be elucidated.