Actions of vitamins A and E and some nicotinic acid derivatives on plasma lipids and on lipid infiltration of aorta in cholesterol-fed rabbits.

Marked hypercholesterolemia and moderate lipid infiltration of the aorta were induced by feeding rabbits a diet containing 1% cholesterol + 3% corn oil for 70 days. In the liver the concentration and pool size of cholesterol increased and those of triglycerides (TG) decreased. On dietary addition of vitamin A and vitamin E (44 000 I.U. and 125 mg respectively, once daily for 5 days a week) the following changes were noted in comparison with the fat-fed rabbits not receiving extra addition of vitamins. There was a slight decrease of the levels of plasma cholesterol and an increase of those of plasma TG. The liver cholesterol concentration increased but, according to the concomitant reduction of the liver weight, there was no significant change in lever cholesterol or TG pools. In the aorta the vitamins markedly reduced the lipid infiltrated area as well as the cholesterol content. Both niceritrol** and S-2040 [pyridine-2,5-dicarboxylic acid di(beta-pyridylcarbinol ester)] in a dietary concentration of 0.5% decreased plasma cholesterol by about 20%. This reduction, as well as that induced by the vitamins, was confined to the VLDL-fractions only. S-2040 slightly reduced the cholesterol accumulation in the aorta. In rabbits given both the vitamins and niceritrol or S-2042 there was an additive reduction of plasma cholesterol. Here the nicotinic acid derivatives were partly able to counteract the increases of plasma TG induced by the vitamins. In the aorta the combination vitamins + S-2042 but not that of vitamins + niceritrol tended to give a better protection than the vitamins alone. On a normal diet vitamins A + E significantly increased the liver cholesterol concentration and pool and decreased the liver TG pool, but did not affect the other parameters. Possible mechanisms for the prophylactic action of the vitamins against lipid infiltration of the aorta of cholesterol-fed rabbits are discussed.