Abstract
Control and treated beagle and random-source dog hearts obtained from 119 toxicological experiments were evaluated histologically to study the incidence and characteristics of a microscopic inflammatory lesion specific to the extramural coronary arteries. The lesion occurred in 23% of the experiments. The incidence was 2.3% of the control and treated beagle hearts examined. In the control begales, it was present in 3.1% of males and 1.3% of females and in the treated beagles, in 1.8% males and 2.8% females. It occurred in 4.7% of the random-source animals. While not visible grossly, histologically, the solitary lesions were characterized by adventitial infiltrates of mononuclear cells, occasional areas of necrosis with inflammatory cell infiltrates occurring in the mural and subendothelial regions. The latter resulted in prominent separation of the intima from the media. The lesions occurred in the right and left coronary arteries and in the dorsal, circumflex and ventral descending branches of the left coronary artery. Similar vascular lesions were not found in the intramural coronary vessels or in other organs in the affected animals. Expanded sampling of the extramural coronary arteries revealed an incidence of 5–9%. This lesion of focal extramural coronary arteritis was considered idiopathic, and not a manifestation of recently reported polyarteritis syndromes in dogs.