title: Muscle energy metabolism in McArdle's syndrome by in vivo phosphorus magnetic resonance spectroscopy.
abstract: Five patients with McArdle's syndrome were examined by phosphorus magnetic resonance spectroscopy (31P-NMR). Adenosine triphosphate (ATP) levels at rest were reduced by 22%, but did not fall further during exercise or contracture. The slope of work rate versus inorganic phosphate/phosphocreatine (Pi/PCr) was 42 +/- 8 joules/min/Pi/PCr in three patients without muscle wasting, compared with 13 and 16 in patients with atrophy (normal, 30 to 50 joules/min/Pi/PCr). Recovery from exercise showed similar rates in patients (postischemic exercise 1.03 +/- 0.17, post-aerobic 1.63 +/- 0.17 PCr/Pi units per minute) and controls (1.0 +/- 0.2 and 1.8 +/- 0.2, respectively) independent of intracellular pH. Infusion of glucose improved exercise kinetics by 163 to 190%, but an oral load of protein had no effect. We conclude that (1) muscle mitochondria operate normally in vivo in this glycogenolytic disorder, suggesting a sufficient alternate fuel supply. (2) Blood-borne glucose may serve as one alternate fuel for the "second wind" phenomenon. (3) ATP control mechanisms are altered only at rest. (4) Recovery from exercise is relatively pH-independent.
mesh_terms: D000328:Adult; D004734:Energy Metabolism; D006008:Glycogen Storage Disease / Q000378:metabolism*; D006012:Glycogen Storage Disease Type V / Q000175:diagnosis / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D009132:Muscles / Q000378:metabolism* / Q000473:pathology; D010758:Phosphorus; D005082:Physical Exertion
chemical_list: D010758:Phosphorus