Fibrous plaques in the aortas of adult female rhesus monkeys (Macaca mulatta).

Lesions in the abdominal aorta were found in 36 of 40 mature female rhesus monkeys given various oral contraceptive steroids and in 8 of 10 monkeys of a non-treated control group. The lesions consisted of proliferation of subendothelial smooth muscle cells and collagen, often with fragmentation of the internal elastic lamina, forming a plaque. These occurred also, in order of descending frequency, in thoracic aorta, aortic arch, femoral and iliac arteries, and the carotid and pulmonary arteries. They appear statistically unrelated to steroid treatment and lack correlation with body weight and blood cholesterol levels.