Pathologic changes noted in rats fed D&C Red No. 10 [monosodium salt of 2-(2-hydroxy-1-naphthylazo)-1-naphthalenesulfonic acid] for two years

Abstract

Two hundred and fifty 3-week-old Osborne-Mendel rats divided into 5 groups of 50 rats each, and each group equally divided by sex, were started on a 2-year feeding experiment on D & C Red No. 10 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 of test rats. Percentage of rats surviving on the 2-year test was increased by the addition of the color to the diet. Slight to moderate splenic enlargement was noted in 1% and 0.25% feeding level rats. Grossly 42% of the rats had pneumonia, 17% had nephritis, 17% had pituitary lesions, and 43% of the females had mammary tumors. Other incidental gross pathology randomly distributed among these 250 rats included lymphosarcoma in 7 rats, subcutaneous tumors in 5 males, endometrial sarcomas in 4 females, thyroid tumors in 4 rats, testicular tumors in 3, hepatic tumors in 2, abdominal lipoma in 1, leukemia in 1, ovarian tumor in 1, cystic ovaries in 5, ovarian abscesses in 2, and 1 rat each with a splenic infarct, a large abdominal hematoma, and a foot-pad granuloma. Approximately 800 tissue sections from these 250 rats were prepared for microscopic study. Histopathology attributable to D & C Red No. 10 toxicity occurred only in the spleen and bone marrow. Since survival of the test animals is considered to be more important to these animals than their slight to moderate splenic and bone marrow hyperplasia, it is apparent that D & C Red No. 10 had a beneficial effect in this experiment. However, because of the undesirable side effects of splenomegaly and bone-marrow hyperplasia at the 1% and 0.25% feeding levels, the 0.05% level should be considered the “no-effect” level.