Role of hypocapnia in the alveolar surfactant increase induced by free fatty acid intravenous infusion in the rabbit.

Intravenous infusion of free fatty acid (FFA) produces an increase in the alveolar surfactant pool of the rabbit and pulmonary edema, hyperventilation, hypoxemia and hypocapnia. Previous studies suggested that alveolar PCO2 would be a regulator of intracellular storages of surfactant. In order to study the role of hypocapnia in the increase of lung surfactant in our experiments we administered 20 mg FFA X kg-1 X min-1 i.v. to rabbits breathing room air (n = 10) or 5% CO2, 21% O2, 74% N2 (n = 7). Disaturated phosphatidylcholine (DSPC) was determined in bronchial-alveolar lavage fluid as index of alveolar surfactant content, 5% CO2 in the inspired air prevented the hypocapnia and blocked the increase in DSPC induced by FFA (p less than 0.01). Pulmonary edema post-FFA was not changed by 5% CO2 administration. We conclude that hypocapnia produced by hyperventilation during FFA infusion would be an important factor in the increase of DSPC observed after FFA infusion.