On the postulated peroxidation of unsaturated lipids in the tissues of vitamin E-deficient rats

Abstract

1. The micro-iodimetric method has been used to study some factors affecting the concentration of lipid peroxides in the adipose tissue of vitamin E-deficient rats.2. Cod-liver oil methyl esters (CLOME) or maize oil methyl esters (MOME) with peroxide values ranging from 3 to 330 μ-equiv./g were given by mouth to vitamin E-deficient rats deprived of food before and after the dose. Lipid peroxides did not accumulate in the adipose tissue of these rats.3. Experiments with dietary CLOME and MOME of varying peroxide values (2–230 μ-equiv./g) showed that exogenous lipid peroxide accumulates in the adipose tissue when the rats received these lipids at 10% in the diet for 4 weeks, but not if the dietary concentration was only 4% or if the diet with 10% lipid was given for 5 days only.4. Rats were given dietary CLOME for 4 weeks. Their adipose tissue was then found to contain about 50 μ-equiv. lipid peroxide/g. They were divided into three groups. One group was given a fat-free diet and, after 10 days, the adipose tissue concentration of lipid peroxide had decreased to about 10 μ-equiv./g. The other groups were given the fat-free basal diet supplemented with vitamin E or DPPD (N,N′-diphenyl-p-phenylenediamine). Neither supplement significantly affected the rate of disappearance of the peroxides from the adipose tissue.5. It was shown that neither α-tocopherol nor DPPD reacted with the lipid peroxides of CLOME or MOME in vitro, at room temperature or even after 65 h at 37°.6. It was concluded that unsaturated lipids do not become peroxidized after incorporation into the adipose tissue of vitamin E-deficient rats. Lipid peroxides taken up from the diet into the adipose tissue are not of fleeting existence, having a half-life of about 6 days. Dietary vitamin E probably prevents the accumulation of exogenous lipid peroxides in the adipose tissue by reinforcing the barrier to their absorption in the gut.7. These studies provide further evidence that current concepts of lipid peroxidation in vitamin E-deficient animals are incorrect. In fact, vitamin E-deficient animals have low concentrations of peroxide in their adipose tissue, unless they have received large amounts of unsaturated lipid for long periods, and the role of vitamin E in controlling this concentration is not due to any effect on peroxidation in vivo.