Immunocytochemical hormonal features of pituitary adenomas of aging Wistar male rats

Pituitary adenomas were the most common grossly visible naturally occurring neoplasms found in over 27% of rats surviving beyond 17 months of age. Twenty-three pituitary adenomas, fixed in buffered neutral formalin and embedded in paraffin, were tested for the presence of prolactin (PRL), growth hormone (GH) and thyroid stimulating hormone (TSH) using the unlabeled peroxidase-antiperoxidase method. The adenoma cells in 6 (26%) of the 23 tumors stained with two or three of the tested hormones, but clear evidence that individual neoplastic cells contained more than one hormone was not found. These findings suggest that in aging male Wistar rats the spontaneous pituitary adenomas may originate from undifferentiated cells, PRL-, GH- and TSH-cells in a diminishing order of frequency.