Historical data are presented for neoplasms and related proliferative lesions from 1,170 Sprague-Dawley rats that served as controls in 9 carcinogenicity (2 year) studies conducted in the Safety Evaluation Facility of Ciba-Geigy Corporation, Summit, New Jersey. The most common neoplasm was pituitary adenoma, which occurred in 62.2% of the male and 84.7% of the female rats. Incidences of other neoplasms that occurred in more than 6.0% of the rats were, for males, benign pheochromocytoma (19.0%), cutaneous keratoacanthoma (7.9%), pancreatic islet cell adenoma (7.5%), benign testicular interstitial cell tumor (6.5%), and thyroid C-cell adenoma (6.5%). For females these incidences were mammary fibroadenoma (31.3%), mammary adenocarcinoma (16.8%), and mammary adenoma (6.5%). Focal cortical hypertrophy/cystic degeneration of the adrenal, a focal nonneoplastic lesion of zona fasciculata cells that often degenerate into large cysts, was present in 23.4% of all male and 82.7% of all female rats. Criteria for the differential diagnoses of selected neoplasms and related lesions are presented.

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The oldest members of most short- and long-lived mammalian species develop many similar morphologic changes. This suggests that the combined occurrence of a variety of age-associated lesions in a group can be used as an indicator of its advanced biological age. Males and females from our colony of aging Syrian hamsters were previously shown to have an equally high incidence of atrial thrombosis and myocardial degeneration, despite the females' much shorter life-span. Other age-associated lesions were then examined histopathologically to determine whether females age faster than males. Hepatic, renal, and splenic amyloidosis were more severe in females than in males and became so at an earlier age. Degenerative lesions were also found in adrenals, thyroids, and brains of both sexes. Atrophy was especially severe in the thymus. The incidence of malignant neoplasms, most of which were of lymphoreticular origin, was similar in both sexes. Female hamsters may age faster than males if biological age can be assessed by these morhologic criteria.

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SummaryMany of the aging Syrian hamsters maintained in our Division spontaneously develop atrial thrombosis accompanied by a consumption coagulopathy. The 50% mortality level is reached earlier by females (16 months) than by males (24 months). The incidence of thrombosis increases with age, beginning at 13.5 months in females and at 21.5 months in males, and the overall incidence (73%) is nearly the same for both sexes. Bilateral ventricular hypertrophy was found in thrombosed hearts. The hearts of most aged hamsters, whether thrombosed or not, had myxoid valvular thickenings and myocardial degeneration. Myodystrophic changes included hypertrophied nuclei, cytoplasmic vacuolation, fiber atrophy, and finally replacement fibrosis. Thrombosis probably resulted from local blood stasis secondary to cardiac failure. These hamsters may be an especially useful model for comparative study of the effects of aging and myocardial degeneration on spontaneous thrombosis.