Effects of prostacyclin (PGI2) on hypoxic pulmonary vasoconstriction in the conscious adult sheep.

The effects of prostacyclin (PGI2) on alveolar hypoxic pulmonary vasoconstriction were investigated in the conscious adult sheep. In our model, hypoxia also produced increases in pulmonary arterial pressure (PPA) and pulmonary vascular resistance (PVR), indicating pulmonary vasoconstriction. PGI2 was injected rapidly as a 0.5 microgram/kg bolus via the right atrium in five sheep during normoxia and hypoxia. During normoxia, PGI2 increased PPA and cardiac output, and decreased systemic arterial pressure (PSA), systemic vascular resistance (SVR) and PVR. Left atrial pressure did not change. During hypoxia following PGI2 administration, PPA decreased, CO increased, and PVR decreased, suggesting dilator action on the pulmonary resistance vessels. As the same time PSA and SVR decreased, suggesting dilator action on the systemic resistance vessels. However, the degree of the decline in PVR caused by PGI2 was much greater during hypoxia than during normoxia. The decreases in PSA and SVR induced by PGI2 were not significant between hypoxia and normoxia. These findings confirm that PGI2 decreases pulmonary and systemic vascular resistances in normoxic and hypoxic sheep. Moreover, during hypoxia, associated with the increased PPA and PVR, the administration of PGI2 appears to be particularly effective in "normalizing" these parameters.