Studies on prolactin-secreting cells in aging rats of different strains. II. Selected morphological and immunocytochemical features of pituitary tumors correlated with serum prolactin levels.

Sixty pituitary tumors from 151 aging rats of the BN/BiRij strain, the WAG/Rij strain and their F1 hybrid were studied light microscopically. The lowest tumor incidence (18%) was found in the BN/BiRij strain, the highest incidence (71%) in the WAG/Rij strain. In the F1 hybrid the incidence (45%) was intermediate between those of the parental strains. With a hematoxylin-phloxin-saffron (HPS) staining two tumor types, i.e. hemorrhagic and solid could be distinguished. Immunocytochemical staining with anti-r-PRL antiserum revealed a positive reaction in the hemorrhagic and a negative reaction in the solid type, whereas staining with anti-sh-GH and anti-ACTH generally were negative. In animals with hemorrhagic as well as with solid tumors elevated serum PRL levels were found, although some differences were noticed. Serum levels in females of the WAG/Rij strain with hemorrhagic adenomas were significantly higher than the levels in females with solid adenomas. In the same strain, age-related differences in PRL levels were found. Significantly higher serum PRL levels were found at the age of 26-32 months than in older animals. The same tendencies were noticed in both other strains.