Decrease in urinary excretion of 3-methylhistidine by patients with Duchenne muscular dystrophy during glucocorticoid treatment.

Seven patients, aged 10-17 years, with Duchenne muscular dystrophy were treated orally with prednisolone (PSL) at a dose of 0.8-1.0 mg/kg per day for 8 weeks. During the treatment their muscle strength, serum creatine kinase (CK) activity, serum levels of myoglobin (Mb), and urinary excretion of 3-methylhistidine (3-MeH) and glycine (Gly) were measured serially. In all the patients, the motor function or muscle strength improved, and the serum CK activity and Mb level decreased during PSL treatment. Urinary excretion of 3-MeH, a unique constituent of muscle contractile proteins, decreased to 51-63% of the baseline value in weeks 6-9 after the start of PSL administration, and returned to the baseline level in week 12. The ratios of 3-MeH to creatinine and to Gly also decreased during the treatment. Urinary excretion of Gly, which is ubiquitous in all tissues including muscle, did not decrease during the treatment. These findings suggest that PSL inhibits proteolysis of muscle contractile protein.