Young female pastel mink and young female Sprague-Dawley rats were injected intraperitoneally on 3 sequential days with 50 mg/kg of either 2,4,2′,4′ tetrachlorobiphenyl (TCB) or 3,4,3′,4′-TCB and sacrificed after 7 days. Two control groups were established for each species; one allowed free access to food, and one pair-fed to the 3,4,3′,4′-TCB-treatment group. Heart blood was collected from each mink immediately after sacrifice. A complete set of tissues was collected from all animals and placed in buffered formalin. The rats displayed no clinical signs of illness following the administration of either congener, nor were there any significant gross or microscopic lesions created in this species. Mink in the 2,4,2′,4′-TCB and control groups remained free of clinical signs and significant gross or microscopic lesions. Mink in the 3,4,3′,4′-TCB group developed anorexia within 48 hr after the initial injection, and depression and melena by Day 4. Necropsy on Day 7 revealed a severe necrotizing enteritis with moderate to marked villus atrophy and fusion in the small intestines of all mink in this treatment group. The epithelial necrosis generally spared the basal one-third of the mucosa, and the deep crypt epithelium was often moderately hyperplastic. The mechanism by which 3,4,3′,4′-TCB causes this unique lesion is unknown.
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