Effect of prednisone on protein metabolism in Duchenne dystrophy.

Prednisone improves strength in Duchenne dystrophy and changes the natural history of the disease. We studied the in vivo effects of prednisone (0.75 mg.kg-1.day-1) on muscle and whole body protein metabolism in six patients with Duchenne dystrophy and three patients with Becker dystrophy. Patients were admitted to the Clinical Research Center for study and consumed a constant flesh-free diet. Strength was measured by manual and quantitative muscle testing. Fractional muscle protein breakdown was estimated by the ratio of 3-methylhistidine to creatinine excretion determined in three consecutive 24-h urine collections. Whole body protein kinetics were studied in the postabsorptive state using a primed continuous infusion of L-[1-13C]leucine. Fractional muscle protein synthesis was determined from tracer incorporation into noncollagen muscle protein obtained by needle biopsy. After 6-8 wk of prednisone treatment, average muscle strength increased by 15% (P < 0.04), and 24-h creatinine excretion (an index of muscle mass) increased by 21% (P = 0.002). 3-Methylhistidine excretion decreased by 10%, but the change was not statistically significant. The ratio of 3-methylhistidine to creatinine excretion decreased by 26% (P < 0.04). Fractional muscle protein synthesis and whole body protein synthesis and breakdown did not change significantly. We conclude that the beneficial effect of prednisone on strength in Duchenne dystrophy appears to be associated with an increase in muscle mass, which may be mediated by inhibition of muscle proteolysis rather than stimulation of muscle protein synthesis.