Pathologic changes noted in rats fed D&C Red No. 9 for two years

Abstract

Two hundred and fifty 3-week-old Osborne-Mendel rats divided into 5 groups of 50 rats each, each group equally divided by sex, were started on a two-year feeding experiment on D&C Red No. 9, which was mixed into the diet at levels of 1%, 0.25%, 0.05%, 0.01% and 0% (controls) and fed ad libitum. The color had no apparent effect on the growth rate, mortality, or occurrence of tumors in the test rats. Hemoglobin levels were slightly lowered and red blood cell abnormalities were observed in rats on the 1% and 0.25% feeding levels. At autopsy, survivors on the 1% feeding level showed moderate splenomegaly and rats on the 0.25% level showed slight splenomegaly. Rats on these two feeding levels had less chronic nephritis than did either control rats or rats on the two lower feeding levels. Grossly 58% of the rats had pneumonia, 18% had nephritis, 18% had pituitary lesions, and 29% of the females had mammary tumors. Other incidental gross pathologic changes randomly distributed in these 250 rats included lymphosarcoma in 6 rats, epidermal carcinomas in 3 rats, interstitial cell tumors of the testis in 3 males, subcutaneous fibromas in 2 males, and 1 rat each with a thyroid carcinoma, pulmonary adenocarcinoma, cecal fibroma, hepatoma, vaginal tumor, and a uterine polyp. Randomly distributed incidental nonneoplastic gross pathology included adrenal enlargement in 12 rats, uterine or ovarian cysts or abscesses in 11 females, subcutaneous abscesses in 3 rats, foot granulomas in 3 rats, prostatic abcesses in 2 males, mammary hyperplasia in 2 females, and 1 case each of hepatic abscess, pancreatic abscess, mesenteric arteritis, perirenal hemorrhage, and marked testicular atrophy. Histopathologic findings attributable to D&C Red No. 9 feeding consisted of moderate splenomegaly at 1%, slight splenomegaly at 0.25%, and slight bone marrow hyperplasia at both levels. The 1% feeding level rats also showed slightly increased splenic hemosiderosis and some had splenic infarcts. The incidence of nephritis was significantly decreased at the 1% and 0.25% feeding levels; however, pigmentation of the renal tubular epithelium occurred only in rats on these two feeding levels. At 0.05% and 0.01% there were no gross or microscopic pathologic changes attributable to D&C Red No. 9.