Objective: Although the lung can both produce and extract endothelin, its role in regulating plasma endothelin is not settled. Whether the endocardium is able to affect plasma endothelin is also unknown. The first aim of this study was to examine if endothelin concentration in plasma changes when passing through the pulmonary circulation or the left heart chambers. A marked decrease in endothelin concentration has been shown to occur in the aortic arch during early reperfusion following a 10 min mid left anterior descending coronary artery occlusion. A second aim was therefore to investigate whether this decrease was due to removal of endothelin in the pulmonary circulation or through the left heart chambers.
Methods: In seven open chest, pentobarbitone anaesthetised pigs blood was obtained from the pulmonary artery, the left atrium, and the aortic arch at control conditions and at 10 and 20 min reperfusion following a 10 min coronary occlusion. Endothelin measurements were performed using an endothelin 1-21 specific [125I] assay system (RPA 555).
Results: At control conditions there was no difference in endothelin concentration in blood obtained from the pulmonary artery [3.9 (2.7-5.2) fmol.ml-1, median (95% confidence interval)] and the left atrium [3.8 (2.8-5.8) fmol.ml-1], whereas there was a significantly higher endothelin concentration in the aortic arch [4.9 (3.8-7.2) fmol.ml-1]. At 10 min reperfusion following the 10 min coronary occlusion there was still no difference in endothelin concentration between the pulmonary artery [4.3 (2.8-6.0) fmol.ml-1] and the left atrium [4.1 (2.7-5.7) fmol.ml-1]. However, in contrast to the increase observed before myocardial ischaemia, the endothelin concentration was significantly reduced in the aortic arch [2.8 (2.4-4.4) fmol.ml-1] compared to the left atrium. At 20 min reperfusion, all endothelin concentrations had returned to preischaemic values.
Conclusions: These findings suggest a role for the left heart chambers in regulating the endothelin concentration in blood entering the aorta.