INHIBITION OF ENDOTHELIUM-DEPENDENT RELAXATION BY FREE HEMOGLOBIN IN THE HUMAN INTERNAL THORACIC ARTERY

Hemolysis and postoperative hypertension are well recognized complicat ions of cardiopulmonary bypass (CPB). The rise in the concentration of total and free hemoglobin is directly related to the duration of CPB. It is well established that free hemoglobin binds and inactivates end othelium-derived relaxing factor, and the authors have studied the eff ects of low concentrations of free hemoglobin on the endothelium-depen dent and endothelium-independent relaxation of the human internal thor acic artery (ITA). in the presence of free hemoglobin the endothelium- dependent relaxation induced by acetylcholine was reduced by 80% with 0.5 muM free hemoglobin (P<0.01) and by 52% with 0.1 muM free hemoglob in (P<0.05). Sodium nitroprusside, endothelium independent, produced r elaxation of almost 100%. These results indicate that relatively low c oncentrations of free hemoglobin significantly inhibit endothelium-dep endent but not endothelium-independent relaxation. This may influence blood flow in the ITA and may be a contributory factor in postoperativ e hypertension.