Extracellular amino acids as markers of myocardial ischemia during cardioplegic heart arrest

Extracellular levels of amino acids in the myocardial interstitium are sens itive indicators of myocyte function. Lowered ATP leads to a rapid extracel lular appearance of amino acids with a high intra- to extracellular concent ration ratio, such as taurine and glutamate. Nitrogen fluxes are reflected by glutamine, while alanine, glycine, serine and leucine are markers of pro teolysis. In addition, degradation of membrane phospholipids is reflected b y other primary amines, such as phosphoethanolamine. The time course of the se changes was determined before, during and after cardioplegic heart arres t. Two regions of the heart were monitored in 20 patients by means of micro dialysis sampling. After only 20 min of heart arrest, extracellular taurine , glutamate and phosphoethanolamine increased transiently up to 25 times th e basal level. Ten-20 min later, glutamine increased by 6 times. A doubling of alanine, glycine, serine and leucine levels took place 30 min after rel ease of the aortic cross-clamp. After 2 h, all were at levels similar to th ose recorded 15-30 h later. Levels of taurine and glutamate in the anterior wall of the heart correlated significantly with those of its lateral wall. The response to surgery and heart arrest was studied in a group of patient s with ischemic heart disease as well as in another group of patients, who underwent heart surgery for nonischemic reasons. The response of taurine an d glutamine was significantly higher for the patients with ischemic heart d isease, in spite of a shorter mean time of heart arrest. No sex differences were recorded. High levels of amino acids coincided frequently with clinic al events, which were suggestive of ischemia, but were also recorded in a f ew patients without diagnosed events. We conclude that monitoring of extrac ellular amino acids is valuable for evaluation and development of cardiopro tective strategies.