Comparison of aorta and pulmonary artery: II. LDL transport and metabolism correlate with susceptibility to atherosclerosis.

The pulmonary artery and the aorta are similarly susceptible to atherosclerosis in rabbits. However, the mechanism(s) that accounts for this is not yet known. This study investigated the hypothesis that one or more aspects of arterial low-density lipoprotein (LDL) transport and metabolism might explain the similar susceptibility of the aortic arch and pulmonary artery to atherosclerosis and the increased susceptibility of these arterial regions compared with the descending thoracic aorta. We determined permeability to LDL, rates of LDL degradation, and concentrations of undegraded LDL for the intima-media of normal rabbits and those fed cholesterol for approximately 8 days. Intima-media permeability did not differ between corresponding arterial regions of normal rabbits and rabbits fed cholesterol for 8 days and was similar for the aortic arch and pulmonary artery. Rates of LDL degradation and concentrations of undegraded LDL for the intima-media were influenced by cholesterol feeding. These measures were reduced in fractional terms but increased in absolute terms as a result of hypercholesterolemia, without differences between corresponding parameters for the pulmonary artery and aortic arch. However, permeability to LDL, rates of LDL degradation, and concentrations of undegraded LDL were increased for the intima-media of the aortic arch compared with the descending thoracic aorta. Similar, although not always significant, trends were evident for the comparison of the pulmonary artery and descending thoracic aorta. Differences in LDL transport and metabolism and changes after feeding cholesterol for 8 days parallel the relative susceptibility to atherosclerosis for the three arterial regions studied. These results support the role of arterial LDL transport and metabolism in atherogenesis and potentially provide a mechanistic explanation for the differences in susceptibility to atherosclerosis for these three arterial regions.