The rate of flux of cholesterol from plasma to aortic wall has been measured in normal and diabetic rats given an atherogenic diet. At any given time, there were significant linear relations between plasma cholesterol concentration and influx rate and between influx rate and aortic cholesterol concentration, These relationships altered with time in a manner to suggest the development of an inhibition to cholesterol influx. Diabetic animals had higher levels of plasma cholesterol, but the interdependencies among the three parameters noted were qualitatively the same as those of the nondiabetics, suggesting that the increased susceptibility of diabetics to the development of atherosclerosis is due to more severe hypercholesterolemia. The flux rate of cholesterol into the aorta was much higher than the net rate of cholesterol deposition, indicating that a large part of the influx is in the form of exchange with a labile pool. On replacement of the atherogenic diet by a normal diet, the plasma cholesterol fell promptly to normal while the aortic cholesterol fell more slowly and did not return to the normal level. The results applied equally to unesterified and total cholesterol and to cholesterol of whole plasma or low density lipoproteins.

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