A physiologic role for the esterified cholesterol transfer protein: in vivo studies in rabbits and pigs

The observation that pig plasma is deficient in esterified cholesterol transfer activity has been exploited in an attempt to establish an in vivo role for the esterified cholesterol transfer protein. The plasma high density lipoproteins (HDL) of pigs and also of rabbits (a species known to possess an active esterified cholesterol transfer protein) were labeled with 3H in the esterified cholesterol moiety and with 125I in the apoprotein moieties and reinjected into the respective species. In both rabbits and pigs, the removal of 125I from the recipient HDL fraction was parallel to that from the whole plasma, with negligible 125I appearing in other plasma lipoprotein fractions. In the pig, the removal of esterified 3H-cholesterol from the recipient HLD was very similar to that of 125I; there was only minimal appearance in other lipoproteins. In the rabbit, however, there was a major in vivo transfer of esterified 3H-cholesterol from HDL to other fractions. It has been concluded that an active esterified cholesterol transfer protein is probably necessary to achieve the in vivo transfer of esterified cholesterol from HDL to other plasma lipoproteins.