Myocardial uptake and release of substrates in patients operated for unstable angina : Impact of glutamate infusion

• Objective - To study cardiac uptake and release of substrates and the influence of intravenous glutamate in patients operated for unstable angina requiring intravenous nitrates. Design - Nineteen patients were randomized to blinded infusion of glutamate or saline. Arterial-coronary sinus differences of substrates were measured before cardiopulmonary bypass (CPB) and during early reperfusion. Results - Before CPB the only major substrates that were extracted by the heart in the saline group were free fatty acids (FFAs). During reperfusion uptake of glucose and glutamate was found but FFAs remained the major substrate extracted by the heart. Initially transient low oxygen extraction and lactate release were found. Conversion to lactate uptake was not observed. Glutamate infusion was associated with an uptake of glutamate and in contrast to the control group there was also uptake of lactate before CPB and at the end of the study period. Conclusion - The metabolic situation before CPB with a reliance on myocardial FFA uptake is less than ideal with regard to ischemia. Early reperfusion was characterized by dynamic changes and a shift towards myocardial glucose uptake but FFAs remained the major substrate extracted. The qualitative findings associated with glutamate infusion agree with previous animal and human studies but have to be interpreted cautiously due to lack of flow measurements.

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