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Alleviation of Methionine Toxicity in Young Male Rats Fed High Levels of Retinol¹

Department of Nutrition and Food Science, University of Arizona, Tucson, Arizona 85721

The effect of excess retinol intake (150 to 1,000 IU per g diet) for 7 to 10 days on methionine toxicity was investigated with young male rats. This retinol treatment appeared to be non-toxic because it did not affect growth and food intake of the rats receiving the treatment. However, after the treatment, the retinol treated rats were partially protected against methionine toxicity as indicated by better growth and food intake as compared to those not receiving the treatment. The magnitude of the alleviation was less apparent in rats trained to eat for 2 hours a day than in those fed ad libitum. Weight change of retinol treated and nontreated rats fed a diet containing 10% casein plus 2% L-methionine ad libitum for 12 days was 51 and 17 g, respectively, while rats fed a 10% casein diet containing a required amount of methionine gained 89 g. Retinol treatment caused a marked increase in the storage of liver retinol and, also, about 50% decrease in the concentration of methionine in plasma of rats fed high (2 or 3%) methionine diets. However, the oxidation of [U-¹⁴C]methionine to ¹⁴CO₂ was not significantly increased by the retinol treatment. Depressions in growth and food intake of rats fed a diet containing high levels (3 to 5%) of L-cystine or S-methyl-L-cysteine (0.47 to 2.4%) were not alleviated by the retinol treatment. These observations suggest that the transsulfuration pathway beyond cysteine and also the S-adenosylmethionine independent pathway (J. Biol. Chem. 253, 7844, 1978) were not affected by the retinol treatment.

KEY WORDS: • methionine toxicity • retinol • S-methyl-L-cysteine • rat

¹ Supported in part by Nutrition Foundation Grant 477. The University of Arizona Agricultural Experiment Station Journal Paper No. ????.

Manuscript received 24 April 1978.