Hemodynamic responses to prostacyclin (PGI2) in the conscious sheep

Hemodynamic responses to prostacyclin (PGI2) were studied in sheep in the conscious state as well as under pentobarbital-halothane anesthesia. PGI2 in doses of 0.02-1.0 microgram/kg were administered as a bolus into the right or left atrium in the conscious sheep. PGI2 decreased systemic arterial pressure (PSA), systemic (SVR) and pulmonary vascular resistance (PVR) and increased cardiac output (CO) and heart rate (HR) in a dose-dependent manner. The changes of each parameter were almost similar regardless of the sites of administration. Pulmonary arterial pressure (PPA) was increased. There was no change in left (PLA) or right atrial pressure (PRA). A bolus administration of 0.5 microgram/kg of PGI2 in the anesthetized sheep produced a decrease in PSA, SVR and PVR, and increase in CO and HR. PPA remained unchanged when administered into the right atrium and increased slightly when administered into the left atrium. PLA and PRA did not change. Comparing hemodynamic responses to 0.5 microgram/kg of PGI2 of the conscious and anesthetized states, decrease in PSA was smaller and increases in CO and HR were greater in the former. Decreases in SVR and PVR were similar in both states. Increase in PPA was greater in the conscious sheep. This data confirms that PGI2 dilates the systemic as well as the pulmonary circulation of the sheep and an inactivation of this compound in the lungs is minimal. Furthermore, it may be suggested that general anesthesia significantly alters hemodynamic responses to PGI2 in the sheep.