[The lung, producer of prostacyclin]

Under physiological conditions prostacyclin (PGI2) is the main metabolite of arachidonic acid that is generated and released by lungs. The generation of PGI2 by lungs seems to be a continuous process and, therefore, PGI2 can be considered as a circulating hormone whose concentration is by 100--200 pg/ml higher in arterial blood than in mixed venous blood. The generation of PGI2 by lungs can be augmented by angiotensin ll, bradykinin and arachidonic acid provided that low concentrations of these substances are infused into pulmonary artery. Also air pulmonary emboli and mechanical hyperventilation stimulate the lungs to generate more prostacyclin. Respiratory stimulants such as lobeline or almitrine are even more effective in this respect. It is proposed that this para-endocrine function of the lung constitutes an important physiological mechanism that protects coronary and cerebral arteries against thrombosis and atherosclerosis. The efficacy of this mechanism can be increased by pharmacological procedures. A link between ventilatory and non-ventilatory function of the lungs is proposed. Hyperventilation increases the hormonal function of the lungs i.e. stimulates generation of prostacyclin. On the other hand we also propose a link between these functions of the lungs and homeostasis in cardiovascular system.