RECIRCULATION OF PROSTACYCLIN (PGI2) IN THE DOG

Abstract

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-PGF_lat. 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 (ig 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.