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C3H mice including aged retired breeding females, aged virginal females, young virginal females and young males were examined for the incidence and severity of pulmonary calcification. Pulmonary calcification appeared in aged females, but not in young mice of either sex, and the lesions in aged breeders were more severe and frequent than in aged virgins. These results indicate that spontaneous pulmonary calcification is observed in aged females of the C3H strain. The findings of increased incidence and severity of pulmonary lesions in aged breeders suggest that pregnancy, delivery and lactation are important enhancing factors. Calcified lesions were also observed in kidney, heart, brain, ovary, choroid plexus, cornea and artery in the animals examined.

A total of 153 female virgin Slc: 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 occurring 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.

Histopathological observations were made on the spontaneous age-related kidney lesion in relation to some biochemical measurements for renal function using male SD rats from 82 to 560 days of age. Although all the rats examined were appearently healthy and had no gross lesions in the kidneys, several renal changes were detected histopathologically in the kidneys. The lesions occurred initially in renal tubules and then in glomerulus and in interstitial tissues successively increasing in severity with age. There was a correlation between the degree of the histopatholigical changes and the excreted amount of protein and sodium in the urine. The urinary protein was first detected at 34 days of age increasing with age. For rats of over 395 days of age, the urinary protein was greatly variable in amount among individuals. The negative correlation between urinary protein levels and those of serum albumin and urinary potassium was significant.