An ultrastructural comparison of carcinogen-associated and spontaneous aortic lesions in the cockerel.

Ultrastructural studies were performed on arteriosclerotic aortic lesions in cockerels given weekly injections (10 mg/kg, 4-36 weeks of age) of the carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) and on spontaneous lesions in age-matched controls. Lesions were observed in all animals. Regardless of treatment, lesions of similar size were indistinguishable. They were composed primarily of modified smooth muscle cells, (SMC) which were oriented more randomly than medial SMCs. The interstitia were composed mainly of collagen. Lesion cells displayed invaginated nuclei and dense bodies characteristic of normal SMCs but were modified in shape and displayed fewer myofilaments and more rough endoplasmic reticulum than did normal SMCs. Larger lesions, found only in DMBA-treated animals, contained relatively few cells and more collagen. These cells, which contained dense bodies but not myofilaments, were flatter and more uniformly oriented than cells in smaller lesions. Thus, there is a size continuum of arteriosclerotic lesions in the cockerel. Chronic DMBA treatment accelerates size increases of spontaneous lesions rather than inducing the formation of new lesions. In this system, DMBA appears to "promote" rather than "initiate" the lesions.