An automatic method for determination of urinary and myofibrillar 3-methylhistidine: fractional rate of myofibrillar protein breakdown in rats fed on casein as source of protein.

An automatic, more rapid and simplified analytical system for determination of 3-methylhistidine in urine and skeletal muscle is described, which may be applied to more extensive studies of large number of samples within a reasonable period of time and constitutes a powerful tool in understanding the dynamics of protein metabolism in the intact organism. This procedure allows the analysis of 3-Methylhistidine by ion-exchange chromatography in 140 +/- 2.5 min using a single column system. The mean urinary 3-Methylhistidine output of rats weighing about 200 g fed on an adequate diet of casein was 0.84 +/- 0.02 microM/100 g BW, and the mean values for skeletal muscle in these animals were 0.74 +/- 0.03 microM/g tissue. The fractional rate of myofibrillar protein breakdown assessed by the urinary 3-Methylhistidine was 0.028 +/- 0.002%.