Objective: To study the changes in amino acid content of left ventricles of patients during cardiac surgery that involves cardiopulmonary bypass and cold cardioplegia.
Design: Biopsy specimens (up to 10 mg wet weight) from the left ventricle of 30 patients undergoing coronary artery bypass graft and valve replacement surgery on cardiopulmonary bypass (protected by cold cardioplegia with St Thomas' solution) were taken immediately before the infusion of the cardioplegic solution and just before the removal of the cross clamp, and were analysed for their amino acid content.
Results: Of the most abundant cellular amino acids in the left ventricle taurine, glutamine, glutamate, and aspartate, but not alanine, showed a significant fall during the period of cross clamping. A rise in intracellular sodium (Na) is known to occur during cold cardioplegic arrest so that an activation of an amino acid/Na efflux, similar to that seen in animal experiments, seems a likely mechanism. The anomalous behaviour of alanine suggests some recovery of metabolism.
Conclusions: The loss of alpha amino acids (by contrast with the loss of taurine) will depress protein synthesis and reduce energy reserves after cardiac surgery. Attempts to preserve the concentrations of intracellular alpha amino acids must be balanced against the need to regulate intracellular Na concentration and hence intracellular pH and calcium ions. The presence of alpha amino acids in the cardioplegic solution (or in a resuscitation solution) should maintain the intracellular concentrations and favour activation of the taurine/Na symport to oppose the rise in intracellular Na concentration. Because the reservoir of tissue taurine is limited, the potential benefits of increasing the concentration of taurine in the heart by diet before surgery and addition of alpha amino acids to the cardioplegic solution merits further assessment.