Improvement in the endothelium-dependent relaxation in hypercholesterolemic rabbits treated with vitamin E

The authors studied the time course of the vitamin E mediated improvement in endothelium-dependent relaxation in hypercholesterolemic rabbits. A total of 40 male New Zealand white rabbits were randomly assigned to hypercholesterolemic (control) and vitamin E treated groups. The latter group was further divided in three subgroups in accordance with the duration of the vitamin E treatment (2, 4 or 6 days) at the end of the experiment. The dose of vitamin E utilized was 50 IU/day administered once a day by gavage. All the rabbits were fed a diet supplemented with cholesterol (0.5%) and coconut oil (2%) for 4 weeks. At the end of this period, the animals were sacrificed and the aorta removed for determination of the cholesterol and malondialdehyde (MDA) contents. The relaxation of the aortic strips in response to acetylcholine was also studied. In addition, the cholesterol and MDA contents of native and oxidized LDL were measured. At the end of the 4th week, the MDA level was significantly reduced in native and oxidized LDL in the rabbits treated with vitamin E for 2 days, while in aortic tissue a reduction was seen after 4 days of treatment. Endothelium-dependent relaxation improved significantly after 6 days of vitamin E administration, and there was a reduction in the total plasma and aortic cholesterol levels during this same period. We conclude that vitamin E at a dose of 50 IU/day for 6 days improves the endothelium-dependent relaxation seen in hypercholesterolemic rabbits. This effect may be mediated through an antioxidant action on LDL particles and on the aortic arterial wall.