[Natural history of the regression of atherosclerosis: from animal models to men].

Numerous studies carried out on animal models (apes excepted) have given encouraging results as regards the regression of experimental atherosclerosis after return to a normal or hypocaloric diet combined or not with various drugs. Regression is more obvious when lesions are recent and less severe: lipid striae disappear in less than 12 months, whereas more advanced and complicated lesions take years to regress. Intracellular lipids and cell alterations vanish more readily than extracellular lipids and alterations of connective and matrical tissues. Excessive accumulation of collagen accounts for the irreversibility of complicated plaques. Lesions of the intima are less stubborn than those of the media. Involution does not take place at the same time in coronary vessels and in the aorta. In non human primates, however, no noticeable regression is observed before several months if not years. In these animals, the degree and rapidity of involution after return to the normal vegetarian diet depend on the severity of the lesions induced, on the degree of fibrosis, on the level of residual hypercholesterolaemia and on the adjunction to the diet of certain drugs such as cholestyramine or alpha-alpha. The results of therapeutic trials conducted in man have not been so good because the patients treated had old and severe atherosclerosis: after a few years' treatment with low-cholesterol diet and appropriate drugs less than 10 p. 100 of them showed a clear-cut angiographic improvement. It is therefore illusory to rely on spontaneous regression when tackling a case of clinically detectable atherosclerosis. A preventive treatment is more promising, since infraclinical lesions may regress.