Effects of strong physical exercise on blood glutamate and its metabolite 2-ketoglutarate levels in healthy volunteers.

Abstract

Excessive concentrations of L-glutamate (glutamate) have been found to posses neurotoxic properties. This study investigates how stress induced by strong physical exercise effects blood glutamate, 2-ketoglutarate, Alanine aminotransferase (ALT) and Aspartate Aminotransferase (AST) levels. The relationship between muscle damage caused by strong physical exercise and blood glutamate levels was also examined. Twenty-two healthy volunteers engaged in intense veloergometry ("spinning") for a duration of 60 minutes. Two 10 minute peaks of extremely intense exercise were performed at 10 minutes and 50 minutes after the start of exercise. After 60 minutes of exercise, volunteers were monitored for an additional 180 minutes in resting conditions. Blood samples for determination of glutamate and 2-ketoglutarate levels were collected prior to exercise and then every 30 min for entire experiment. Blood samples were also taken at those time points to measure glutamate, 2-ketoglutarate, AST, ALT, creatine phosphokinase (CPK), myoglobin, lactate and venous blood gas levels. Blood glutamate levels were significantly elevated throughout the exercise session (P less than 0.001) and then returned to baseline levels at the cessation of exercise. 2-ketoglutarate, a product of glutamate metabolism, reached significantly elevated levels at 30 minutes (P less than 0.01) from the start of exercise and remained elevated up to 240 minutes post exercise initiation (P less than 0.001). AST and ALT levels were elevated at 60 minutes when compared to baseline. AST levels remained elevated at 240 minutes, unlike ALT levels which returned to baseline values at 240 minutes. Strong physical exercise leads to a significant elevation in blood glutamate, most likely as a result of skeletal muscle damage. 2-ketoglutarate was also found to be elevated for long periods of time, reflecting an ongoing process of glutamate breakdown. Elevated concentrations of AST and ALT in plasma reflect the importance of these enzymes in the maintenance of stable blood glutamate concentrations.