The enolase isoenzyme composed of the β subunit (αβ or ββ enolase) is distributed predominantly in the heart and skeletal muscles. To see whether it may be a useful indicator of myocardial damage, concentrations of β-enolase (the β subunit of enolase) were determined in serial blood samples taken from 18 patients who underwent mitral valve replacement, using a highly sensitive enzyme immunoassay method. They were compared with those of creatine kinase MB isoenzyme (CK-MB) in the same samples. The mean arterial β-enolase concentration was 6.60 (SD 3.84) ng·ml-1 at the beginning of anaesthesia. It increased rapidly after reperfusion and rose to > 100 ng·ml-1 at 2 h post-reperfusion. It remained high until 12 h post-reperfusion, and then decreased slowly. The plasma β-enolase concentrations were significantly higher in coronary sinus samples than in arterial samples in the early phase after reperfusion. Since plasma carbonic anhydrase III, which is known to be localised only in the skeletal muscle, did not increase during the surgery, we suggest that the major portion of the elevated plasma β-enolase was derived from heart muscle. Plasma concentrations of β-enolase increased as quickly as those of CK-MB after reperfusion. The CK-MB concentrations had returned to normal at 2 d but the β-enolase concentrations remained elevated up to 7 d. These results show that the determination of β-enolase in plasma may be useful for estimating myocardial damage during open heart surgery.
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