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Dietary Oxidized Frying Oil Enhances Tissue -Tocopherol Depletion and Radioisotope Tracer Excretion in Vitamin E-Deficient Rats^1,2,

Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan 10764

Rats fed a diet containing 15% oxidized frying soybean oil (OFO) have been shown to have significantly lower tissue -tocopherol (-T) concentration than rats fed a 15% fresh soybean oil diet. To examine the turnover of -tocopherol, a depletion-repletion experiment and a radioisotope tracer study were conducted. Two groups of male weanling Long-Evans rats were fed vitamin E-deficient diets containing either 15% OFO or 15% vitamin E-stripped fresh soybean oil (control). After 9 wk of depletion, rats fed the OFO diet had significantly higher plasma pyruvate kinase (PK) activity and lower concentrations of -T in RBC, adrenal gland, heart, kidney, liver, spleen, testis and muscle compared with controls (P < 0.05), indicating that the vitamin E-deficient status was aggravated by feeding the OFO diet. After 12 wk, the depleted rats were intraperitoneally injected with a dose of all-rac--T (2.5 mg/rat, dissolved in Vitamin E-stripped corn oil) every other day. Three doses were administered to each rat during the 1-wk repletion period. Plasma PK activity decreased in both groups (P < 0.05) after repletion but that of the OFO rats was still significantly higher than that of the control group. The repleted OFO group also had significantly lower -T concentration in adrenal gland, epididymal fat, liver and spleen than the repleted control group. Two rats from each group that had been vitamin E-depleted for 16 wk were injected intraperitoneally with a single dose of 5-methyl-¹⁴C-RRR--T (740 kBq/kg body weight). During the week after dosing, the radioactivity excreted in urine and feces of the OFO group was 1.3- and 1.7-fold, respectively, that of the control group. Tissue retention of radioactivity was also lower in the OFO rats than in the control rats. The results suggest that more of the -T in the body was catabolized or turned over in rats fed the OFO-containing diet.

KEY WORDS: • oxidized frying oil • vitamin E • rats • depletion • radioisotope tracer

¹ Supported by grant no. NSC 80-0409-B002-82 from the National Science Council, Taiwan, Republic of China.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ Current address: Department of Nutrition, Taipei Medical College, Taipei, Taiwan.

⁴ To whom correspondence should be addressed.

Manuscript received 13 November 1995. Revision accepted 13 May 1996.

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