Recirculation of prostacyclin (PGI2) in the dog.

1 The inactivation of prostacyclin (PGI2) in the circulation of anaesthetized dogs has been studied by the blood-bathed organ bioassay technique. 2 Spiral strips of bovine coronary and rabbit coeliac or mesenteric artery detected concentrations of PGI2 of 2 to 5 ng/ml. These tissues were insensitive to concentrations at least 200 fold higher of 15-oxo-PGI2 and 6-oxo-PGF1alpha. 3 PGI2 assayed on bovine coronary artery, rabbit coeliac artery or rat stomach strip, had a half life in blood of 3.0 +/- 0.3 min, indicating non-enzymatic degradation. 4 No disappearance could be detected by bovine coronary artery when PGI2 was infused across the lungs (0.1 to 0.5 microgram kg-1 min-1). However, PGI2 was partially inactivated in passage through vascular beds of hindquarters and liver. 5 Of PGI2 infused into the aorta 35 to 65% escaped inactivation in one complete circulation. Therefore, endogenous PGI2 released from the lungs may function as a circulating hormone.