SURFACTANT REGULATES PULMONARY FLUID BALANCE IN REPTILES

Reptilian lungs are potentially susceptible to fluid disturbances beca use they have very high pulmonary fluid filtration rates. In mammals, pulmonary surfactant protects the lung from developing alveolar edema. Reptiles also have an order of magnitude more surfactant per square c entimeter of respiratory surface area compared with mammals. We invest igated the role of reptilian surfactant 1) in the entry of vascularly derived fluid into the alveolar space of the isolated perfused lizard (Pogona vitticeps) lung and 2) in the removal of accumulated fluid fro m the alveolar space of the isolated perfused turtle (Trachemys script a) lung by both the pulmonary venous and lymphatic circulations. The f lux of fluorescent (fluorescein isothiocyanate) inulin from the vascul ature into the alveolar compartment increased 60% after the removal of surfactant, but capillary fluid filtration over a 10-min period was n ot affected. Surfactant removal decreased alveolar inulin clearance by both the pulmonary venous circulation and the pulmonary lymphatic sys tem similar to 1.5- and S-fold, respectively. In reptiles, fluid flux from capillary to air space must occur indirectly via the interstitium . In the absence of surfactant, this may result in interstitial drying , which affects both pulmonary venous and pulmonary lymphatic clearanc e of alveolar fluid.