AN ATYPICAL AORTIC ATHEROSCLEROTIC LESION IN CYNOMOLGUS MONKEYS DURING HYPERCHOLESTEROLEMIA - A PROTECTION BY SMOOTH-MUSCLE CELLS AGAINST ADVANCED LESIONS

This study focuses on the fortuitous discovery of an atypical atherosc lerotic lesion in four of 49 male adult cynomolgus monkeys (macacus fa scicularis) which were maintained for a long time at a high level of h ypercholesterolemia, and in seven of 19 female cynomolgus monkeys exam ined from the second to the 24th week of hypercholesterolemic diet: th is lesion was in formation or already mature during this period of die t. This atypical lesion was formed by a collagen and elastic network s urrounding synthetic smooth muscle cells without fibrofatty or fibrous plaques. Lipids were occasionally seen in the inner intima. The lesio n appeared early (from the third week of diet). Once established, its morphology did not change. It became more extensive, but was not compl icated by lipid overload in spite of prolonged, permanent hypercholest erolemia. This response to hypercholesterolemia is interesting because the activity of the smooth muscle cells differs from that observed in the classic lesion: they intervene earlier, their replication is very marked and rapid, their elastin secretion is greater and remains cons tant over time, and their phagocytic properties are reduced. This expe rimental study examines the installation and the maintenance of this l esion and raises the problem of its origin.