The Influence of Temperature, Phylogeny, and Lung Structure on the Lipid Composition of Reptilian Pulmonary Surfactant

Abstract

The lungs of all air-breathing vertebrates contain a form of pulmonary surfactant that lines the alveolar air—water interface where it modifies the interfacial surface tension. These pulmonary surfactants all consist of varying amounts of phospholipids (saturated and unsaturated) and cholesterol. The extent of variation between vertebrate groups and between species within a vertebrate group has been attributed to differences in factors such as phylogeny, body temperature, habitat, and lung structure. The influence of these factors on amphibian surfactant composition and function has been studied, but the reptiles, which comprise a polyphyletic group of vertebrates, have never been critically examined. The surfactant lipid composition from species belonging to the three groups of reptiles, the Archosauria (crocodiles), Lepidosauria (snakes and lizards), and Anapsida (turtles), has been determined. New data is presented in conjunction with already published data to create an evolutionary framework that concentrates particularly on the influence of phylogeny, body temperature, and lung structure on the composition of the surfactant lipids. Large amounts of pulmonary surfactant were found in all species of tiles. All species lavaged at 23°C (except C. atrox) demonstrated DSP/PL ratios of 23–33%. Animals with multicameral lungs exhibited an elevated CHOLIDSP ratio compared with species with unicameral lungs. In all groups, phosphatidylcholine (PC) was the dominant (60–80%) phospholipid. Phosphatidylserine and phosphatidylinositol (PS/PI) and sphingomyelin (S) represented the other phospholipids, while phosphatidylglycerol (PG), lysophosphatidylcholine (LPC), and phosphatidylethanolamine (PE) were occasionally observed. In two species of lizards (C. nuchalis and P. vitticeps), the saturated fatty acid, palmitic acid (16:0), was the dominant tail group on the phospholipids. Oleic acid (18.1) was the dominant monounsaturated fatty acid, whereas polyunsaturates comprised about a fifth of the total fatty acid profile. Short-term (4 h) changes in temperature did not affect the relative proportions of the fatty acids in either species. Comparison of the current data with previously published literature suggests that phylogeny and habitat do not significantly influence surfactant lipid composition, but body temperature and to a lesser extent lung structure are important determinants of reptilian surfactant lipid composition.

Key Words:

• cholesterol
• crocodiles
• lizards
• phospholipiok
• phylogeny
• reptiles
• snakes
• surfactant
• temperature
• turtles