Idiopathic extramural coronary arteritis in beagle and mongrel dogs.

Hearts obtained from 119 toxicological experiments on dogs during a 21-year period (1965-1986) were evaluated histologically to determine the incidence and characteristics of focal microscopic inflammatory lesions of the extramural coronary arteries. Lesions were encountered in 23% of 119 experiments. The average overall incidence was 2.3% of 1,905 control and chemically treated male and female beagle hearts (3.1% of male and 1.3% of female control beagles, and 1.8% of male and 2.8% of female treated beagles). Lesions were seen in 4.7% of 127 random-source mongrel dogs. Histologically, lesions were characterized by adventitial infiltrates of mononuclear cells, areas of mural necrosis, and inflammatory cell infiltrates in both mural and subendothelial regions. In the latter region, fibrosis developed separating the intima from the internal elastic membrane. Lesions occurred in the right and left coronary arteries and in the dorsal, circumflex, and ventral descending branches of the left coronary artery. Vascular lesions were not present in the intramural coronary vessels or in vessels of other organs in affected animals. More extensive sampling of the extramural coronary arteries revealed an incidence of 5-9%. The lesion of focal extramural coronary arteritis was idiopathic, and not a manifestation of the polyarteritis syndrome of dogs.