Impaired muscle energy metabolism in uremia as monitored by 31P-NMR.
Uremic patients often complain of fatigue and muscle weakness. In order to elucidate the abnormalities of energy metabolism in the muscles of such patients, we measured the concentrations of phosphocreatine (PCr), inorganic phosphate (Pi) and adenosine triphosphate (ATP) as well as the intracellular pH in skeletal muscles by 31P-NMR at rest, during aerobic and anaerobic exercise and during recovery in 15 uremic patients (7 non-dialyzed patients and 8 dialyzed patients) and 6 control subjects. At rest, there was no difference in intracellular pH between the uremic patients and controls, but the concentrations of PCr and ATP in the skeletal muscle were lower in the uremic patients. However, during aerobic exercise, the uremic patients showed a rapid decrease in intracellular pH and a delay in its recovery. They also revealed an increased PCr utilization during aerobic exercise and its delayed resynthesis during recovery. During anaerobic exercise, the uremic patients, especially non-dialyzed patients, displayed a slower decrease in pH than the controls and a delay in its recovery. An increased PCr utilization during anaerobic exercise and a delayed resynthesis during recovery were also demonstrated. These findings suggest that the aerobic and anaerobic energy productions in uremic patients are impaired and that the energy production of the muscle depends on anaerobic glycolysis during exercise. Hemodialysis apparently facilitates recovery of the inhibited enzyme activities of oxidative phosphorylation and glycolysis in uremic patients.