PULMONARY SURFACTANT LIPIDS IN THE FAVEOLAR AND SACCULAR LUNG REGIONS OF SNAKES

We examined the composition and function of pulmonary surfactant located within the faveolar and saccular regions of the garter snake Thamnophis ordinoides and the rattlesnake Crotalus atrox lung While the faveolar region is well vascularized and septated and is used in gas exchange, the saccular lung is a thin-walled smooth bag with very little vascularization that functions as a bellows and in gas storage. Both regions of the lungs of the two snake species contained large amounts of surfactant The rattlesnake faveolar lung contained 2419.9+/-260.0 mu g of phospholipid per gram of wet lung mass, a value among the largest ever recorded for any species. However, snake faveolar lung surfactant is markedly different from all other vertebrate surfactants reported to date because it contains relatively little cholesterol (3%-8%). Faveolar lung surfactant of the rattlesnake had a greater phospholipid saturation level than that of the garter snake. The phospholipid profile of garter snake faveolar lung surfactant was very similar to that reported for most other nonmammalian vertebrates, with phospha tidylcholine (PC) the predominant phospholipid (64%), phosphatidylglycerol (PG), phosphatidylethanolamine (PE), and sphingomyelin (S) either absent or present only in brace amounts (1%-4%), and intermediate (17%) levels of phosphatidylinositol (PI). The phospholipid profile of rattlesnake faveolar lung surfactant, on the other hand differed greatly from that of most other vertebrates in that it contained unusually high levels of lysophosphatidylcholine (LPC) and S (12%-18%), whereas PG and PI were virtually absent (0%-1.4%). Removal of surfactant by lavage increased the opening pressure (the initial pressure required to commence the inflation of a collapsed lung) of both regions of the garter snake lung (faveolar region 1.32-4.51 cm H2O; saccular region, 1.55-2.19 cm H2O). However the rattlesnake faveolar region did not collapse even after lavage, and an opening pressure was never obtained The opening pressure for the rattlesnake saccular lungs (2.78 cm H2O) was not increased by lavage (3.0 cm H2O). The filling pressures were greater for the faveolar lung than for the saccular lung for both species. Filling pressure of the two lung regions was not affected by lavage in either snake.