PHOSPHOLIPIDS IN MEIBOMIAN GLAND SECRETION

The bulk of the lipid layer overlying the aqueous portion of the preco rneal tear film is composed of polar and nonpolar components. The nonp olar lipids have been the subject of numerous studies; however, the po lar lipids have remained relatively uncharacterized. The polar lipids ate thought to contain surfactant phospholipids that are critical to t he spreading of a lipid film over the aqueous layer, by providing an i nterface between this layer and the nonpolar lipids. The purpose of th e present study is to identify and quantitate the phospholipid complem ent of meibomian gland secretion which provides the tear film with pho spholipids. Meibomian gland secretion was collected from rabbits and p hospholipids identified and quantitated by P-31 nuclear magnetic reson ance spectroscopy. Ten phospholipids were detected from meibomian glan d secretion: diphosphatidylglycerol, dihydrosphingomyelin, ethanolamin e plasmalogen, phosphatidylethanolamine (PE), phosphatidylserine, sphi ngomyelin, lysophosphatidylcholine, phosphatidylinositol, alkylacylpho sphatidylcholine, and phosphatidylcholine (PC). The two major phosphol ipids were PC and PE, together comprising nearly 60 % of the total pho spholipid profile. The nature and relative concentrations of the meibo mian gland secretion phospholipids are congruous with a surfactant rol e at the aqueous-lipid interface and, considering the physical chemist ry of the tear film, suggest that the phospholipids should be organize d in a very flat or planar configuration.