Pulmonary Extraction of 5-Hydroxytryptamine and Norepinephrine before and after Cardiopulmonary Bypass in Man

Pulmonary extraction of 14 C-5-hydroxytryptamine and 3 H-norepinephrine was estimated in patients undergoing aortocoronary saphenous vein grafting. Identical mixtures of both amines were administered intravenously before Cardiopulmonary bypass and again just after bypass. Immediately after each injection, 6 ml of blood was withdrawn into tubing, at a constant rate, simultaneously from both the pulmonary artery and the left atrium. Each set of tubing was then divided into six segments, and the 3 H and 14 C content of each segment was measured. In this manner, total isotope collected and blood isotope concentration as a function of time at the two sampling sites were compared directly. Before bypass in every patient studied, less 5-hydroxytryptamine and norepinephrine were withdrawn on the left than on the right of the lungs, implying pulmonary extraction of both amines. In nine patients, the mean percent extraction was 65 ± 4% for 5-hydroxytryptamine and 23 ± 5% for norepinephrine ( P < 0.005). After bypass, the percent extraction of both norepinephrine and 5-hydroxytryptamine was increased in all but one patient; values for norepinephrine were increased to a realtively greater extent. These data represent a direct demonstration of 5-hydroxytryptamine and norepinephrine extraction by human lungs and also suggest that total Cardiopulmonary bypass may alter the process.