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Determination of Carnitine Turnover in Choline-deficient and Cold-exposed Rats¹

Department of Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan 48824

Two experiments were conducted to study the body pool size and turnover rate of carnitine in rats. The turnover of carnitine was determined by injection of a tracer dose of L-[methyl-¹⁴C]carnitine. In experiment 1, carnitine body pool size and turnover in rats fed a choline-deficient basal diet were compared with values obtained from rats fed the basal diet supplemented with choline. These rats were maintained at 22°. In experiment 2, carnitine body pool size and turnover were determined in cold-exposed (2°) rats fed the choline-deficient basal diet. Carnitine body pool sizes of rats maintained at 22° and fed the choline-deficient basal diet and the choline-supplemented diet were 35.6 and 41.8 µmoles/100 g body weight, respectively. Carnitine body pool size of rats maintained at 2° and fed the choline-deficient basal diet was 43.3 µmoles/100 g body weight. Turnover times of the fast and slow turnover pools of carnitine for rats maintained at 22° and fed a choline-deficient basal diet were 6.6 and 56.1 days, for rats fed a choline-supplemented diet, 6.7 and 40.2 days, and for rats maintained at 2° and fed a choline-deficient diet, 2.9 and 36.4 days, respectively. Carnitine turnover times obtained in the present study, using L-[¹⁴C]carnitine, were longer than turnover times obtained with DL-[¹⁴C]carnitine in our previous study (J. Nutr. 104, 782–792). These observations suggest that D-carnitine is not metabolized the same way as L-carnitine, and that D-carnitine is not cleared from the body within 2 days after injection. The results also suggest that carnitine metabolism can be influenced by the amount of choline in the diet and by cold exposure.

KEY WORDS: • carnitine • carnitine turnover • dietary choline • cold exposure • tissue carnitine concentration

¹ Supported by Public Health Service Grant no. HL 14677 from the Heart and Lung Institute, Michigan Agricultural Experiment Station Journal Article no. 6765.

² Present Address: Nutrition Program. School of Public Health, Room M-5170-SPH, 11. The University of Michigan. Ann Arbor, Mich. 48104.

Manuscript received 3 April 1974.