The levels of apolipoprotein-E in hypercholesterolemic rat serum.

The levels of apolipoprotein-C (apo-E) in serum and isolated liproproteins from diet-induced hypercholesterolemic, and to some extent hypertriglycerdemic rats were measured by electroimmunoassay. The hypocholesterolemia was accompanied by a mild hypertriglyceridemia. The apo-E was increased by 60% in the hypercholesterolemic serum with a 5- and 50-fold increase in very low density lipoproteins (VLDL) and low density lipoproteins (LDL) respectively. However, the proportion of apo-E in nascent VLDL isolated from the hepatic Golgi apparatus of hypercholesterolemic rats was significantly decreased. In control serum, 40--50% of the apo-E is found in the density greater than 1.21 g/ml fraction, although this is at least partially due to ultracentrifugation. The aproprotein is absent from the density greater than 1.21 g/ml fraction from hypercholesterolemic serum, suggesting that it is bound more firmly to the lipoprotein complex. It is concluded that the large increases in apo-E in the VLDL and LDL density ranges of serum from hypercholesterolemic rats may in part be accounted for by the utilization of apo-E normally found at higher densities.