Methylhistidine excretion

Time After Exercise Urea Excretion (mmol/kg) 3-Methylhistidine Excretion (nmol/kq) ... 

Calles-Escandon J, Cunningham JJ, Snyder P, Jacob R, Huszar G, Loke J, Felig P. Influence of exercise on urea, creatinuie, and 3-methylhistidine excretion in normal human subjects. Am J Physiol 1984 246 E334-8. 

The smdy of tissue protein breakdown in vivo is difficult, because amino acids released during intracellular breakdown of proteins can be extensively reutilized for protein synthesis within the cell, or the amino acids may be transported to other organs where they enter anabohc pathways. However, actin and myosin are methylated by a posttranslational reaction, forming d-methylliistidine. During intracellular breakdown of actin and myosin, 3-methylhistidine is released and excreted into the urine. The urinary output of the methylated amino acid provides a rehable index of the rate of myofibrillar protein breakdown in the musculature of human subjects. 

Excretion of creatinine, 3-methylhistidine and urea are low, indicating a low rate of protein degradation. 

Soupart s data for histidine excretion are lower than those of Stein and of Evered because they do not include 3-methylhistidine. The data of Stein and Evered include 3-methylhistidine because their figures were obtained with Moore and Stein s 1951 method and not their 1954 method which was used by Soupart (S24). 

Amino acid excretion in urine varies with maturation of renal tubular function. Premature infants, especially during the first week, have a generalized physiological renal aminoaciduria (see Figure 20-2) even at full term, aminoaciduria is more pronounced than in normal adults. In the urine of normal adults, glycine is usually the dominant fraction, with alanine, serine, glutamine, and— in indulgent meat eaters— histidine and 1-methylhistidine present in smaller quantities. In some normal urine, taurine is prominent in others, (3-aminoisobutyric acid is seen. 

The normal pattern of the urine is characterized by the presence of five amino acids which give prominent spots. These are glycine, serine, alanine, glutamine, and histidine. Moderate amounts to traces of lysine, threonine, glutamic acid, taurine, methylhistidine, and j8-aminoiso-butyric acid occur in some normal samples (Fig. 4). Soupart (S42) and Peters et al. (P17) have published data on the urinary excretion of the free amino acids by normal human subjects which provide a useful compilation of the current knowledge in this field (Table 4). 

A severe amino aciduria is usually present. All amino acids normally found in the urine, as well as 1-methyl-histidine and 3-methylhistidine, are excreted in excess in advanced cases. The amino add level in the plasma, however, remains normal [40-45]. 

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