Abstract
Background Inhalational prostacyclins act as strong vasodilators, potentially improving oxygenation by reducing shunt fraction and ventilation-perfusion mismatch. As prostacyclin receptors are known to be present on human erythrocytes, possible direct effects on oxygenation were further explored by examining the sole in-vitro influence of prostacyclins on hemoglobin oxygen (Hb-O2) affinity. Methods Venous blood samples from 20 healthy volunteers were exposed in-vitro to supramaximal doses of epoprostenol, iloprost, and control. By high-throughput measurements, hemoglobin oxygen dissociation curves (ODC) were derived. Hb-O2 affinity, expressed by P50 and hill coefficient, was determined, and analyzed for three subgroups: males (n= 10), females not taking (n= 4) and females taking oral contraceptives (n= 6). Results Epoprostenol significantly decreased P50 in all (27.5 (26.4 - 28.6) mmHg and 24.2 (22.7 - 25.3) mmHg; p<0.001) thereby increasing Hb-O2 affinity. Inversely, iloprost merely showed significant effects in females taking oral contraceptives where P50 was markedly increased and therefore Hb-O2 affinity decreased (28.4 (27.9 - 28.9) mmHg and 34.4 (32.2 - 36.0) mmHg; p<0.001). Conclusion Prostacyclin-receptor stimulation and subsequent cAMP mediated ATP release from erythrocytes might explain the effect of epoprostenol on Hb-O2 affinity but the reason for the sex hormone modified iloprost effect remains unclear. This finding is of great interest, as contraception is recommended for women taking iloprost. Being aware of potentially differing effects on Hb-O2 affinity might help select the right prostacyclin (epoprostenol vs. iloprost) depending on the patient and the underlying disease (e.g., acute respiratory distress syndrome vs. peripheral arterial disease).