Objective: To investigate the relationship between resting energy expenditure (REE) and body composition in Duchenne Muscular Dystrophy (DMD). Design: An observational study. Setting: University Research Centre. Subjects: Nine Duchenne children (age range 6 -12 y), mean relative weight 128%, agreed to undergo the investigation and all of them completed the study; Interventions: Assessment of body composition (total body fat and skeletal muscle mass) by magnetic resonance imaging and resting energy expenditure by indirect calorimetry. Main outcome measures: Fat mass (FM; kg and percentage weight), fat-free mass (FFM; kg and percentage weight), muscle mass (kg and percentage weight), resting energy expenditure (kJ=kg body weight and kJ=kg fat-free mass). Results: In Duchenne children fat mass averages 32% and total skeletal muscle mass 20% of body weight. Resting energy expenditure per kg of body weight falls within the normal range for children of the same age range, while when expressed per kg of FFM is significantly higher than reference values. No relationship was found between REE and total skeletal muscle mass. Conclusions:Our results do not demonstrate a low REE in DMD boys; on the contrary REE per kg of FFM is higher than normal, probably due to the altered FFM composition. We suggest that the development of obesity in DMD children is not primarily due to a low REE but to other causes such as a reduction in physical activity and or overfeeding.

Myosin heavy chain (MHC) isoform composition and Ca2+ Mg2+ dependent ATPase activity were determined in myofibrils prepared from skeletal muscles (diaphragm, soleus, plantaris and tibialis anterior) of euthyroid (C), hypothyroid (Tx) and hyperthyroid (T3) rats. Direct comparison between T3 and Tx gave an indication of the maximal effect of thyroid hormones. Significant differences in MHC-1 and MHC-2B proportions and in ATPase activity were found in all muscles. The difference in MHC-2A/X proportion was significant only in soleus, diaphragm and plantaris. When T3 and C were compared, significant variations in MHC isoform composition were found only in plantaris and diaphragm. The comparison between Tx and C showed significant differences in MHC isoform distribution and in ATPase activity in most muscles. The differences in ATPase activity among muscles and among thyroid states were consistent with those in MHC isoform distribution. From the correlations between ATPase activity and MHC isoform distribution the enzymatic activities of individual MHC isoforms were calculated. The results indicate that MHC isoform distribution is controlled by thyroid state in all skeletal muscles and that changes in MHC isoforms distribution are accompanied by proportional changes in ATPase activity.

Creatinine concentration in 24-h urine has been proposed as an indirect measure of body skeletal muscle mass (SMM). We attempted to correlate urinary creatinine levels with SMM in eight patients with Duchenne muscular dystrophy, a progressive disease in which the degree of muscle wasting parallels the rate of progression. Magnetic resonance imaging and a newly developed protocol for image analysis were used for the measurement of SMM. The patients ate a creatine-free diet for the week before urine collection. Creatinine was measured with an enzymatic-colorimetric method. Mean (+/-SD) SMM value was 5.4+/-2.5 kg and urine creatinine levels 205.8+/-96.4 mg/day. Daily urinary creatinine excretion did not correlate with SMM. The simple creatinine determination in urine cannot predict SMM in Duchenne muscular dystrophy.

The aim of this study was to determine (i) whether phosphodiesterase inhibitors influenced ATPase activity of maximally calcium activated cardiac myofibrils and (ii) whether this effect varied in relation to isomyosin composition. Myofibrils were prepared from ventricular myocardium of 2- to 3-month-old rats. ATPase activity was determined at low ionic strength at high (> 7.5) and low (4.4) pCa. Five compounds (amrinone, milrinone, enoximone, piroximone, and rolipram) were examined at concentrations between 10 microM and 1 mM. The results obtained showed that only milrinone and amrinone inhibited ATPase activity; inhibition was dose dependent, and milrinone was more potent than amrinone. To assess whether isomyosin composition might influence the responsiveness of myofibrils to phosphodiesterase inhibitors, the effect of 1 mM milrinone was also determined in myofibrils from hypothyroid rats. According to previous observations hypothyroidism caused an isomyosin shift from V1 to V3 in rat ventricular myocardium. The inhibitory effect of milrinone was lower in myofibrils prepared from hypothyroid rats than in myofibrils from euthyroid rats.

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