Local changes in collagen content in rabbit aortic atherosclerotic lesions with time

A video-microdensitometry method was used to quantify collagen on a pixel by pixel basis at specific locations within atherosclerotic lesions, induced by feeding New Zealand White rabbits a declining cholesterol diet. Probability mapping (done previously) showed the lesions occurred in predictable locations so the age of any one area of a lesion could be estimated. The oldest part of the lesion was on the lateral lip of the flow divider as lesions always developed there first. Serial sections through three lesions showed the distribution of collagen within the plaque. The measurement of all the lesions showed that early lesions had low collagen levels: 3-6% for the intercostals and 8-11% for the renals. Collagen increased consistently with time on the diet to 11-15%, for the intercostal and approximately 17% for the renal. The aorto-renal lesions were more severe; thicker and with a higher percentage of collagen. The greatest collagen content was on the lateral lip of the flow dividers, where controls had intimal thickening. No fibrous caps were seen. This study shows conclusively that collagen is not evenly distributed in lesions, but develops progressively in specific locations of fatty plaques with the duration of cholesterol feeding. Intimal thickening predisposes to early collagen development.