To investigate
purine catabolism in exercising muscles of patients with muscle
glycogen storage disease, we performed ischemic forearm exercise tests and quantitated metabolites appearing in cubital venous blood. Two patients with
glycogen storage disease type V and three with
glycogen storage disease type VII participated in this study. Basal
lactate concentrations lowered in every patient with
glycogen storage disease type V or type VII. Two patients with
glycogen storage disease type VII, who had markedly elevated concentrations of serum
uric acid (14.3 and 11.9 mg/dl, respectively), showed high basal concentrations of
ammonia (118 and 79 mumol/liter, respectively; 23 +/- 4 mumol/liter in healthy controls) and of
hypoxanthine (23.4 and 20.4 mumol/liter, respectively; 2.0 +/- 0.4 mumol/liter in healthy controls). Other patients showed near normal measurements of these metabolites. After forearm exercise,
ammonia,
inosine, and
hypoxanthine levels increased greatly in every patient studied, in contrast with the lack of increase in
lactate levels. The incremental area under the concentration curves for venous
ammonia was 13-fold greater in the
glycogen storage disease group than in controls (1,120 +/- 182 vs. 83 +/- 26 mumol X min/liter). The incremental areas of
inosine and
hypoxanthine were also greater in the
glycogen storage disease group (29.2 +/- 7.2 vs. 0.4 +/- 0.1 and 134.6 +/- 23.1 vs. 14.9 +/- 3.2 mumol X min/liter, respectively). The incremental areas of
ammonia in controls and in
glycogen storage disease patients strongly correlated with those of
hypoxanthine (r = 0.984, n = 11, P less than 0.005). These findings indicated that excess
purine degradation occurred in the exercising muscles of patients with
glycogen storage disease types V and VII, and suggested that the
ATP pool in the exercising muscles may be deranged because of defective glycogenolysis or glycolysis.