Inhibition of Endothelium-Dependent Relaxation by Free Hemoglobin in the Human Internal Thoracic Artery

Abstract

Hemolysis and postoperative hypertension are well recognized complications of cardiopulmonary bypass (CPB). The rise in the concentration of total and free hemo globin is directly related to the duration of CPB.

It is well established that free hemoglobin binds and inactivates endothelium-derived relaxing factor, and the authors have studied the effects of low concentrations of free hemoglobin on the endothelium-dependent and endothelium-independent relaxation of the human internal thoracic artery (ITA).

In the presence of free hemoglobin the endothelium-dependent relaxation induced by acetylcholine was reduced by 80% with 0.5 μM free hemoglobin (P< 0.01) and by 52% with 0.1 μM free hemoglobin (P<0.05). Sodium nitroprusside, endothelium indepen dent, produced relaxation of almost 100%. These results indicate that relatively low concentrations of free hemoglobin significantly inhibit endothelium-dependent but not endothelium-independent relaxation. This may influence blood flow in the ITA and may be a contributory factor in postoperative hypertension.

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