D-Methionine Utilization in Adult Monkeys Fed Diets Containing DL-Methionine

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Abstract
D-Methionine added to nutrient sources is well utilized by rats, chickens, miniature pigs and rabbits but is poorly utilized by infant and adult humans. No data are available on monkeys. Four adult female cynomolgus monkeys (Macaca fasicularis) were fed two different commercially available stock diets for two successive 7-day periods in a randomized cross-over design. One diet provided 0.48 g methionine/100 g feed as protein-bound L-methionine. The other provided 0.43 g methionine/100 g feed, 0.29 g as protein-bound L-methionine and 0.14 g as free DL-methionine. Daily total methionine excretion and urinary methionine isomer composition were determined during the 14-day study period. Mean (± SD) methionione excretion was significantly higher (P ≤ 0.001) in animals fed the stock diet with added DL-methionine (67.4±45.8 µmoles/24 hours) than in animals fed the stock diet without added DL-methionine (0.27±0.29 µmoles/24 hours). Methionine isomer analysis indicated that 97.2% of the methionine excreted by animals fed DL-methionine had the D-configuration, thus 26.8% of ingested free D-methionine was excreted. Postprandial plasma free methionine levels did not differ significantly between groups (P > 0.05). However, 24% of the plasma methionine had the D-configuration in animals fed diets with DL-methionine. D-Methionine utilization was also tested when administered without the L-isomer. Fasted monkeys administered 150 mg D-methionine in water by stomach tube excreted 17% of the administered D-methionine in their urine over the following 24 hours. These data indicate the monkey absorbs and metabolizes D-methionine like man rather than like the rat, chicken, pig or rabbit.