Abstract:A variety of neoplastic and non-neoplastic lesions in F344/DuCrj rats, which were used as control animals in chronic toxicity and carcinogenicity studies conducted at the Biosafety Research Center, Foods, Drugs and Pesticides over a 9 year period, are described. The causes of death of animals which were found dead or that were killed in a moribund condition, as well as age-associated differences in the incidence rate of various lesions at 31, 57, 83, and 109 weeks, were also analyzed. The average number of naturally-occurring tumors per rat was 1.68 in male and 0.92 in female rats. The incidence rate of malignant tumors in all animals was 12.5% in male and 11.4% in female rats. The most common tumors were leukemia and benign tumors of the endocrine and reproductive organs. As for the non neoplastic lesions, chronic nephropathy occurred more frequently in male than in female rats. Other lesions commonly observed were atrophic changes in the thymus and reproductive organs, deposits of hemosiderin or ceroid-like materials in a variety of organs, proliferative or hyperplastic changes of the bile ducts, endocrine and reproductive organs, microgranuloma, angiectasis and dilated or cystic changes in a variety of organs, fatty change in the liver and adrenals, and hepatodiaphragmatic nodules of the liver. Nearly all of the above findings increased in both incidence and severity with age. (J Toxicol Pathol 4: 1.24, 1991)

Out of the 365 young laboratory beagle dogs which were used in 17 toxicity bioassays, 15 cases (4.1%) were diagnosed as having congenital heterotopic gastric mucosa of the small intestine. Its incidence in the male dogs (12 cases out of 187) was higher than in the female dogs (3 cases out of 178). Grossly, the lesions were seen as an ulcerous focus of the small intestine, 25 cm to 88 cm proximal to the ileocecal valve. All of the lesions were quite similar histologically and electron microscopically to the normal gastric mucosa, which are composed of the surface mucous cells, chief cells, parietal cells, mucous neck cells and basal granulated cells of the stomach. And consequently, they were considered to be that of a congenital heterotopic tissue in the small intestine. The only morphological characteristic of these lesions different from the regular gastric mucosa was an association with the tubular structure seen in the basal region of these mucosal layers. These cells were considered to be of mucous-secreting cell origin because of secreting type III mucous evident from paradoxical concanavalin A or periodic acid Schiff stains. They seemed to be protecting the surrounding intestinal mucosa from gastric acid.

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Abstract:A variety of spontaneous lesions found histologically in control Beagle dogs (males: 91, famales; 97) used in toxicity studies that were conducted at the Biosafety Research Center, Foods, Drugs and Pesticides during a 10 year period, are described.All animals were exsanguinated by incision of the axillary artery under sodium pentobarbital anesthesia at the end of each study. Neoplastic lesions included fibrosarcoma of the heart in a female dog at approximately 27 weeks of age (1.0%) and hemangioendothelioma of the spleen in a male dog, also at approximately 27 weeks of age (1.1%).The most common non-neoplastic changes in both male and famale dogs were deposits of amor phous masses at the renal papilla (males; 68.1%, females; 80.4%) and fetal glomerulus in the kidney (males; 53.8%, females; 50.5%). Fatty changes in the renal tubular epithelium of female dogs occurred at an incidence of greater than 50%. Pigment deposition in the spleen, guranulation of the liver, atrophy in the thymus, C-cell hyperplasia of the thyroid gland, and pituitary cysts in male and female dogs were evident at an incidence of greater than 10%. In addition, multinucleated giant cells in the testes, eosinophilic bodies in the renal tubular epithelium in males, cellular infiltration of the parotid gland, and deposits of calcium in the spinal cord of females were seen at incidences of greater than 10%. Atrophy of the thymus and C-cell hyperplasia of the thyroid increased with age. Fetal glomerulus of kidney decreased with age.Other rare, but interesting lesions included: ectopic stomach tissue in the ileum, ductro-insular proliferation of the pancreas, deposits of calcium at the beginning portion of the aorta and in the spinal cord, and hemangiectasis at the atrioventriclar valve of the heart. (J Toxicol Pathol 7: 329-343, 1994)

Historical data are presented for neoplastic and non-neoplastic lesions in B6C3F1 (C57BL/ 6•~C3H) mice that served as controls for short-term toxicity, long-term toxicity and carcinogenicity studies conducted at the Biosafety