Spontaneous pituitary changes and their influence on mammary glands in SD [Sparague-Dawley strain] female rats

A total of 153 female virgin Sic: SD rats aged 13 to 24 months were sacrificed for observation of various spontaneous changes in their pituitary glands. Macroscopic changes observed were swelling, congestion, cysts, and grayish white nodules. The incidence of swelling occuring without marked change decreased with age. Usually the swelling was accompanied by congestion in aged animals. Slight to moderate congestion appeared constantly in animals between the ages of 15 to 24 months, while severe congestion (hematoma) increased with age. The cysts and grayish white nodules rarely appeared. Changes observed under the microscope were diffuse proliferation, nodular hyperplasia and tumors (adenoma and adenocarcinoma) of chromophobe cells, cysts in the anterior lobe and hyperplastic pars intermedia. The incidence of diffuse proliferation decreased with age but that of nodular hyperplasia increased in rats over 21 months of age. Both changes seemed to be transitional to tumors. The tumors increased with age. Microscopically, pituitary tumors were found in 6% of macroscopically normal glands as well as in all of the glands with hematoma. All the rats with pituitary tumors had hyperplastic mammary glands, associated mostly with lactation. This suggests that spontaneous pituitary tumors have a hormonal effect on mammary glands.