Histopathology of spontaneous panarteritis in beagle dogs.

Spontaneous focal panarteritis was noted in small and medium-sized arteries including extramural and intramural coronary arteries, and arteries in bone marrow, leptomeninges of spinal cord, meninges of medulla oblongata and tunica albuginea of epididymis of 17 out of 925 beagle dogs used for various toxicity studies. The arterial lesion consisted of varying inflammatory processes in all of the arterial wall and was characterized by intimal fibrinoid necrosis in acute cases and intimal fibrous thickening in chronic cases with varying population of inflammatory infiltrates in the arterial wall. The infiltrates included plasma cells, lymphocytes, macrophages and neutrophils. Periarterial inflammatory cells of the affected arteries showed positive reactions to IgG or IgM. Morphological similarities between spontaneous and drug-induced arterial lesions might confuse the evaluation for vascular toxicity of various chemicals. Therefore, detailed description of the morphology and distribution of spontaneous arterial lesions in the beagle dogs seems to be important for the pathological basis on safety assessment.