THE INFLUENCE OF TEMPERATURE, PHYLOGENY, AND LUNG STRUCTURE ON THE LIPID-COMPOSITION OF REPTILIAN PULMONARY SURFACTANT

The lungs of all air-breathing vertebrates contain a form of pulmonary surfactant that lines the alveolar air - water interface where it mod ifies the interfacial surface tension. These pulmonary surfactants all consist of varying amounts of phospholipids (saturated and unsaturate d) and cholesterol. The extent of variation between vertebrate groups and between species within a vertebrate group has been attributed to d ifferences in factors such as phylogeny, body temperature, habital, an d lung structure. The influence of these factors on amphibian surfacta nt composition and function has been studied, but he reptiles, which c ompromise a polyphyletic group of vertebrates, have never been critica lly examined. The surfactant lipid composition from species belonging to the three groups of reptiles, the Archosauria (crocodiles), Lepidos auria (snakes and lizards), and Anapsida (turtles), has been determine d. New data is presented in conjunction with already published data to create an evolutionary framework that concentrates particularly on th e influence of phylogeny, body temperature, and lung structure on the composition of the surfactant lipids. Large amounts of pulmonary surfa ctant were found in all species of reptiles. All species lavaged at 23 degrees C (except C. atrox) demonstrated DSP/PL ratios of 23-33%. Ani mals with multichameral lungs exhibited an elevated CHOL/DSP ratio com pared with species with unicameral lungs. In all groups, phosphatidylc holine (PC) was the dominant (60-80%) phospholipid. Phosphatidylserine and phosphatidylinositol (PS/PI) and sphingomyelin (S) represented th e other phospholipids, while phosphatidylglycerol (PG), lysophosphatid ylcholine (LPC), and phosphatidylethanolamine (PE) were occasionally o bserved. In two species of lizards (C. nuchalis and P. vitticeps), the saturated fatty acid, palmitic acid (16:0), was the dominant tail gro up on the phospholipids. Oleic acid (18:1) was the dominant monounsatu rated fatty acid, whereas polyunsaturates comprised about a fifth of t he total fatty acid profile. Short-term (4 h) changes in temperature d id not affect the relative proportions of the fatty acids in either sp ecies. Comparison of the current data with previously published litera ture suggests that phylogeny and habitat do not significantly influenc e surfactant lipid composition, but body temperature and to a lesser e xtent lung structure are important of reptilian surfactant lipid compo sition.