RECIRCULATION OF PROSTACYCLIN (PGI2) IN THE DOG

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Abstract
The inactivation of prostacyclin (PGI2) in the circulation of anaesthetized dogs has been studied by the blood‐bathed organ bioassay technique. 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‐PGFlat. 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. No disappearance could be detected by bovine coronary artery when PGI2 was infused across the lungs (0.1 to 0.5 (ig kg−1 min−1). However, PGI2 was partially inactivated in passage through vascular beds of hindquarters and liver. 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.