Phospholipids identified on the pericardium and their ability to impart boundary lubrication.

Phospholipids have been identified by thin-layer chromatography in appreciable quantities in pericardial fluid taken from 12 dogs and found to include sphingomyelin and phosphatidylcholines, -ethanolamines, -inositols and -serines--the cholines predominating. The extracts, the synthetic surfactants and a mixture of synthetics simulating the extracts were all found to be good lubricants when tested by a standard method. The phosphatidylcholines were capable of reducing friction between two otherwise hydrophilic surfaces by as much as 100- to 200-fold when deposited as an oriented monolayer. A goniometer was used to measure an average contact angle of 33 degrees for a drop of saline placed upon the internal wall of the pericardium, indicating an appreciably hydrophobic surface anticipated if surfactant were directly adsorbed. The results are consistent with the classical theory of "boundary" lubrication (17) as modified (21) to reflect the almost ideal molecular structure of the identified surfactants for adsorption, film cohesion and interaction of fatty-acid chains during sliding. This model is proposed as an alternative to hydrodynamic lubrication in the pericardium and one compatible with several practical aspects such as pericardial rub and the maintenance of normal heart action after pericardectomy.