Transfer of Plasma Lipoprotein Components and of Plasma Proteins into Aortas of Cholesterol‐Fed Rabbits

The arterial influx of esterified and free cholesterol from low density Iipoproteins and very low density Iipoproteins in 20 hyperchoiesteroiemic rabbits was measured simultaneously by the use of Iipoproteins labeled in vivo with [3H]- and [14C]-cholesterol. The simultaneous arterial influx of either [3H]-leucine-labeled very low density Iipoproteins, low density Iipoproteins, high density Iipoproteins, or plasma proteins was also measured in each rabbit. The arterial influx was calculated as intimai clearance, i.e., the influx of a given fraction divided by its plasma concentration. The intimai clearance of low density lipoprotein esterified cholesterol was equal to that for the apolipoproteins of that fraction, which is compatible with an arterial influx of intact low density lipoprotein molecules. The intimai clearance of very low density apolipoprotein or cholesteryl ester was less than that for low density lipoprotein, whereas high density lipoprotein and albumin clearances exceeded low density lipoprotein clearance by 1.5-to 3-fold. The intimai clearances of plasma proteins, high density, low density, and very low density Iipoproteins decreased linearly with the logarithm of the macromolecular diameter. This indicates that the arterial influx of three plasma lipoprotein fractions and of plasma proteins proceeds by similar mechanisms. Apparently the relative intimai clearances of Iipoproteins are more dependent on their size relative to pores or vesicular diameters at the plasma-artery interface than on specific interactions between Iipoproteins and the arterial intimai surface.