Background: The endothelin-1 (ET-1) system plays a pathophysiologic role in patients with pulmonary arterial hypertension (PAH). Results from previous studies assessing the transpulmonary gradient of ET-1 have been inconsistent. The influence of an intravenous epoprostenol infusion on the transpulmonary ET-1 gradient is unknown.
Methods: In a prospective investigation, serum concentrations of ET-1 were measured in 39 consecutive patients (31 women; mean age, 20-77 years) with pulmonary hypertension (33 with PAH) and compared with 20 controls. The effect of intravenous epoprostenol administration on the transpulmonary gradient of ET-1 was analyzed in 13 patients with pulmonary hypertension. Blood samples were taken simultaneously from the pulmonary artery and radial artery.
Results: The serum levels of ET-1 were significantly higher in the arterial (3.9 +/- 1.28 vs 2.53 +/- 0.24 pg/ml, p < 0.001) and mixed venous blood samples (3.9 +/- 1.21 vs 2.52 +/- 0.29 pg/ml, p < 0.001) in patients with pulmonary hypertension than in controls. The arterial/venous ratio of ET-1 in patients (1.0 +/- 0.1) and in the control group (1.0 +/- 0.05) was similar (p = 0.79). During intravenous epoprostenol infusion, there were no changes in the mean transpulmonary ET-1 gradient (0.98 +/- 0.07 vs 0.96 +/- 0.09, p = 0.52), despite significant hemodynamic changes.
Conclusion: The ET-1 radial artery/pulmonary artery ratio of unity indicates a balanced release and clearance of ET-1 across the lung circulation in controls and in patients with different forms of pulmonary hypertension. ET-1 levels across the pulmonary circulation did not change during epoprostenol infusion.