Selective endothelial dysfunction in conscious dogs after cardiopulmonary bypass

It has previously been demonstrated that cardiopulmonary bypass (CPB) causes prolonged pulmonary vascular hyperreactivity (D. P. Nyhan, J. M. Redmond, A. M. Gillinov, K. Nishiwaki, and P. A. Murray. J. Appl. Physiol. 77: 1584-1590, 1994). This study investigated the effects of CPB on endothelium-dependent (acetylcholine and bradykinin) and endothelium- independent (sodium nitroprusside) pulmonary vasodilation in conscious dogs. Continuous left pulmonary vascular pressure-flow (LP-Q) plots were generated in conscious dogs before CPB and again in the same animals 3-4 days post- CPB. The dose of U-46619 used to acutely preconstrict the pulmonary circulation to similar levels pre- and post-CPB was decreased (0.13 ± 0.01 vs. 0.10 ± 0.01 mg · kg^-1 · min^-1, P < 0.01) after CPR. Acetylcholine, bradykinin, and sodium nitroprusside all caused dose-dependent pulmonary vasodilation pre-CPB. The pulmonary vasodilator response to acetylcholine was completely abolished post-CPB. For example, at left pulmonary blood flow of 80 ml · kg^-1 · min^-1 acetylcholine (10 μg · kg^-1 · min^-1) resulted in 72 ± 15% reversal (P < 0.01) of U-46619 preconstriction pre-CPB but caused no change post-CPB. However, the responses to bradykinin and sodium nitroprusside were unchanged post-CPB. The impaired pulmonary vasodilator response to acetylcholine, but not to bradykinin, suggests a selective endothelial defect post-CPB. The normal response to sodium nitroprusside indicates that cGMP-mediated vasodilation is unchanged post- CPB.