Contrasting patterns of spontaneous aortic disease in young and old rabbits

The pattern of spontaneous lipid deposition around aortic branch ostia was mapped in New Zealand White rabbits aged 1 month or 2 to 6 years. The young rabbits were studied within 1 day of weaning, and the older rabbits had been maintained on a low-protein, low-fat diet. Plasma concentrations of total cholesterol for the two groups averaged 75 and 18 mg/dL, respectively. Aortas were fixed in situ at a pressure of 90 to 100 cm H2O, stained with oil red O, and photographed en face under an epifluorescence microscope. Areas of staining contrasted in color with the fixative-stimulated autofluorescence of nondiseased tissue and were mapped by placing grids over the photomicrographs. Disease around intercostal ostia was rare, but two distributions were established by combining data from many branches. In weanlings, staining was seen within a triangular area downstream of the branch. In old animals, this area had the lowest frequency of disease; lesions tended to occur downstream of the spared region, along axes lying to either side of it, and at the lateral and upstream margins of the ostium. Disease was less rare at celiac branches. It occurred mainly downstream of the ostium in weanlings, whereas upstream sites were most affected in old animals, although significant disease remained at the juvenile locations. Earlier reports have described similar age-related distributions of disease in human aortas, consistent with a common underlying mechanism. The distributions also correlate with the spatial variations in arterial transport properties established in previous studies, and may be determined by them.