Determination of factors affecting glutamate concentrations in the whole blood of healthy human volunteers

Background: Abnormally high concentrations of glutamate in brain fluids have been shown to be neurotoxic and correlate with a poor neurological outcome following traumatic brain injury (TBI). Since brain fluid glutamate can be reduced by scavenging blood glutamate, the purpose of this study was to investigate factors that may potentially influence levels of blood glutamate, glucose, and the enzymes glutamate-pyruvate transaminase (GPT) and glutamate-oxaloacetate transaminase (GOT) in healthy individuals. Methods: Factors that were examined included age, gender, time of last meal or drink, and recent consumption of coffee. A total of 112 healthy volunteers between 18 and 70 years of age participated in the study. The average participant was 38 years old, and the sample consisted of 48 males and 64 females. Five milliliters of venous blood was collected from participants' cubital vein and blood glutamate, glucose, GOT and GPT levels were determined. Participants were then asked to complete a questionnaire addressing their gender, age, time of last meal, time of last drink, and whether coffee was consumed within the last 6 hours. Results: Blood glutamate concentrations were significantly higher in males than in females (P<0.001) and may be due to effects of estrogen and progesterone. Concentrations of GOT were significantly higher in males than in females (P<0.01). Concentrations of GPT were significantly higher in males than in females (P<0.01). There were no other significant differences demonstrated. Conclusions: Understanding the factors that affect blood glutamate levels may give new insight into mechanisms that protect the brain from excess glutamate and result in a better neurological outcome following TBI.