Pulmonary metabolism of endothelin 1 during on-pump and beating heart coronary artery bypass operations

Background: Coronary artery bypass operations are associated with increased circulating levels of the powerful vasoconstrictor endothelin 1. The pulmo nary circulation is an important site for both production and clearance of endothelin 1. Lung endothelial injury resulting from cardiopulmonary bypass could modify pulmonary endothelin 1 metabolism through an increase in prod uction, a reduction in removal, or a combination of both. Methods: Pulmonary endothelin 1 kinetics were quantified by using the indic ator-dilution technique in patients undergoing coronary artery bypass graft ing with (n = 11) or without cardiopulmonary bypass tie, beating heart; n = 10). Mixed venous endothelin 1 levels were also measured in samples from t he pulmonary artery, and systemic levels were obtained from the radial arte ry. Results: Pulmonary artery endothelin 1 levels were similar before and after cardiopulmonary bypass, with means of 1.59 +/- 0.37 pg/mL and 1.33 +/- 0.1 5 pg/mL (P =.45), respectively. Systemic endothelin 1 levels, however, incr eased after bypass from 1.64 +/- 0.22 pg/mL to 2.07 +/- 0.16 pg/mL (P =.01) . In the beating heart group, endothelin 1 levels before and after the oper ation were similar in the pulmonary artery (1.25 +/- 0.27 pg/mL and 1.45 +/ - 0.31 pg/mL, respectively; P =.38), as well as in the radial artery (1.70 +/- 0.26 pg/mL and 1.73 +/- 0.35 pg/mL, respectively; P =.92). The capacity to clear endothelin 1 from the pulmonary circulation, as computed from the permeability-surface area product for endothelin 1, was not affected by ca rdiopulmonary bypass before and after the operation (25.19 +/- 2.67 mL/s an d 23.12 +/- 4.39 mL/s, respectively; P =.49). It was similar and also unaff ected in the beating heart group. Conclusion: Coronary artery bypass grafting with cardiopulmonary bypass is associated with an increase in systemic endothelin 1 levels. The mechanism involved is not related to a decreased pulmonary clearance of endothelin 1 from the systemic circulation but rather to an increased endothelin I relea se by the lungs.