D‐Methionine Utilization in Young Miniature Pigs, Adult Rabbits, and Adult Dogs

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Abstract
Rats and chickens, unlike man, utilize D-methionine efficiently. We have studied urinary excretion of methionine isomers in young miniature pigs, adult rabbits, and adult dogs given D-methionine in an attempt to find an animal model that, like man, utilizes the D-isomer poorly. Six-week-old miniature pigs ingesting a protein-free diet were infused with 8.5% amino acid solutions differing only in methionine isomer content (L- VS DL-) to supply amino acid requirements. Each solution was infused for a 2- or 3-day period in a cross-over design. Plasma methionine levels were significantly higher (p = 0.01) during infusion of the solution providing DL-methionine, with 25% of total plasma methionine present as the D-configuration. However, urinary methionine excretion was similar with both solutions, with D-methionine utilization calculated as greater than 99%. Adult rabbits ingesting DL-methionine (0.14 g/100 g food) showed good utilization of D-methionine, excreting > 1.3% D-isomer in the urine. Mixed breed dogs given 1.25 g D-methionine in their drinking water excreted >0.4% of ingested D-methionine in the urine. These data indicate that the pig, rabbit, and dog utilize D-methionine efficiently, behaving like the rat and chicken rather than man.