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Glucose arteriovenous differences across muscle in McArdle's disease

Studies of glucose arteriovenous (AV) differences across skeletal muscle in subjects with McArdle's disease (myophosphorylase deficiency) demonstrated normal values during mild exercise even though no increase in venous lactate could be found. Thus, substrate availability appeared not to have exceeded the capacity for aerobic metabolism. In contrast, low AV differences of glucose were present with ischemic exercise. These data support the thesis that phosphorylase activity within skeletal muscle is essential to allow for adequate glycolysis with ischemic work, and that excess glucose and circulating insulin provide insufficient intracellular glucose for this purpose. We interpret the diminished membrane transport of glucose under this condition as secondary to altered cell function.These studies offer an explanation for the inability of patients with McArdle's disease to maintain sustained strenuous exercise despite the availability of adequate circulating glucose.