The in vivo transfer of free and esterified cholesterol from plasma into the arterial wall of hypercholesterolemic rabbits.

With a new technique based on the simultaneous use of 3H and 14C-cholesterol, the fluxes of free and esterified cholesterol into the thoracic aorta of the hypercholesterolemic rabbits have been measured. By additional use of 3H-leucine as tracer for apoproteins, it was shown that esterified cholesterol in plasma enters the arterial tissue mainly as part of a lipoprotein influx. In contrast, only between 20 and 90% of the influx of free cholesterol could be accounted for by an influx of plasma lipoproteins. The excess probably represents an exchange of free cholesterol between the plasma lipoproteins and the intimal surface of the artery. Some 5-40% of the esterified cholesterol which had entered the artery during a 3-6 hours period was hydrolyzed in the artery during that period, whereas only negligible amounts of newly-entered free cholesterol was esterified. The arterial influx of very low, low and high density lipoproteins or albumin was determined in the same animal. The influx of each fraction was expressed as an intimal clearance, i.e., the influx divided by its plasma concentration. The intimal clearances of these macromolecules decreased linearly with the logarithm of their diameters. This suggests that the arterial influx of plasma lipoproteins and of albumin proceed by the same mechanism, which involves a steric hindrance for these macromolecules in the influx pathway.