Comparison of aorta and pulmonary artery .1. Early cholesterol accumulation and relative susceptibility to atheromatous lesions

In rabbits, the pulmonary artery and the aorta are susceptible to atherosclerosis. However, susceptibility of the pulmonary artery, compared with the aortic arch, to atherosclerosis and the relationship between the accumulation of cholesterol during the early stages of atherogenesis and the development of atheromatous lesions for these arterial regions remain to be clarified. Cholesterol concentrations for the pulmonary artery and aorta were measured in normal rabbits and in rabbits fed a 0.5% cholesterol diet for 8, 12, and 16 days and 17 weeks. In normal rabbits, the rank order of arterial cholesterol concentrations was pulmonary artery>aortic arch>descending thoracic aorta, with concentrations of total and nonesterified cholesterol 17% and 25% (both P<.05) greater, respectively, for the pulmonary artery than for the descending thoracic aorta. Rank order remained the same during 16 days of cholesterol feeding, but differences between arterial regions were exaggerated. After rabbits were fed cholesterol for 16 days, total and esterified cholesterol concentrations were 57% and 920% (both P<.01) greater, respectively, for the pulmonary artery than for the descending thoracic aorta, with much smaller differences between the aortic regions. In contrast, after rabbits were fed cholesterol for 17 weeks, concentrations of total, esterified, and nonesterified cholesterol were similar for the pulmonary artery and aortic arch, but these forms of cholesterol were increased 100%, 130%, and 53% (all P<.03), respectively, for the aortic arch compared with the descending thoracic aorta. Cholesterol concentrations for the pulmonary artery were positively associated with those for the aortic regions during the first 16 days of cholesterol feeding, but for rabbits fed cholesterol for 17 weeks the associations were either negative or absent. These results indicate that relative rates of cholesterol accumulation in the pulmonary artery and aorta differ at different stages of atherogenesis and suggest that the balance between processes that deliver cholesterol to, and remove cholesterol from, the artery may change in different ways in these arterial regions during atherogenesis.