Prostacyclin is not a circulating hormone.

Gas chromatography with electron-capture detection of the extensively purified pentafluorobenzyl derivative of 6-oxo-PGF1 alpha was used to determine prostacyclin in blood. Neither human peripheral plasma or whole blood, nor blood drawn directly from the human heart (blood from the right and left atrium which is comparable to pulmonary artery and vein blood), contained any detectable prostacyclin (less than 20 pg/ml). Even hyperventilation did not result in detectable PGI2-formation. During intravenous infusion of PGI2 into one arm, large amounts were found in blood drawn from the other arm. Increased levels were also found during severe infection and in endotoxin shock. These results lend no support to theories based on the concept that prostacyclin is a circulating hormone under normal conditions.