Immuno-electron-microscopic study of the prolactin cells in the pituitary gland of male Wistar rats during aging.

Prolactin cells were identified by means of immunocytochemistry with protein-A gold as a marker on ultrathin sections of the pituitary gland of young (3-4 months), middle-aged (16-19 months), and aged (26-30 months) male Wistar rats. Point-counting volumetry revealed that the prolactin (PRL) cell-volume density in middle-aged rats was significantly increased in comparison to the volume densities in young and aged rats. Within the PRL-cell population, four types of PRL cells were distinguished on the basis of the shape and size of their secretory granules. During aging, dramatic changes occurred in the relative volumes of the four cell types. The volume percentage of cells with round granules (type I, granule diameter 150-250 nm, and type IIA, granule diameter 250-350 nm) increased from +/- 30% in young rats to +/- 90% in old rats. The volume percentage of cells with round and polymorphic granules (type IIB; granule diameter 350-400 nm and type III; granule diameter 500-600 nm) decreased from +/- 70% in young rats to +/- 7% in old rats. Age-related changes in serum PRL levels were not found. It is concluded that although during the life span of the male Wistar rat considerable changes in PRL-cell volume densities and in the ratios of PRL-cell types occur serum, PRL levels remain more or less constant.