Analysis of 1- and 3-methylhistidines, aromatic and basic amino acids in rat and human urine

A procedure based on automated amino acid analysis has been developed to simultaneously quantify 1-methylhistidine (1-MH), 3-methylhistidine (3-MH), tyrosine, phenylalanine, tryptophan, lysine, histidine and arginine levels in human and rat urines. Deproteinized urine samples containing amino acids in the range 1-10 nmol were analyzed using single-column methodology with ninhydrin detection. Standard curves produced correlation coefficients greater than or equal to 0.99 with duplicate analyses agreeing to within +/- 1.9%. Quantitative recovery was ensured by using L-alpha-amino-beta-guanidinopropionic acid as an internal standard. Elution was accomplished in less than 90 min at pH 5.7 with sodium citrate buffers at 45 degrees C and 65 degrees C. Since 3-MH in the rat is acetylated at the alpha-amino group, rat, but not human, urine ultrafiltrates required acid hydrolysis prior to analysis. The utility of the technique of analysis of 1-MH and 3-MH in human urine was demonstrated for an adult male on a meat-free diet for 21 days; urinary excretion rates for 3-MH and 1-MH were determined to be 3.06 +/- 0.10 and 0.72 +/- 0.07 mumol/kg body mass/day, respectively. The technique was also used to measure the effect of disuse atrophy of rat skeletal muscle which induced a 40-60% increase in 3-MH. The procedure is also highly suited for measurement of urinary aromatic and/or basic amino acids.