The lung as a generator of prostacyclin

Under physiological conditions prostacyclin is the main metabolite of arachidonic acid that is generated and released by the lungs. In man and in cat prostacyclin seems to be a circulating hormone whose concentration is 100-200 pg ml-1 higher in arterial blood than in mixed venous blood. Generation of prostacyclin by lungs can be increased by angiotensin II, bradykinin and arachidonic acid provided that low concentrations of these substances are infused into the pulmonary artery. Air pulmonary emboli and mechanical hyperventilation stimulate the lungs to generate more prostacyclin. Respiratory stimulants such as lobeline or almitrine are also effective prostacyclin releasers from the lung. It is proposed that this para-endocrine function of the lung protects coronary and cerebral arteries against thrombosis and atherosclerosis while pharmacological amplification of the pulmonary release of prostacyclin may constitute a new means of treating thromboembolic diseases.