Lubricating effect of sialomucin and hyaluronan on pleural mesothelium

Coefficient of kinetic friction () between rabbit visceral and parietal pleura, sliding in vitro at physiologicalvelocities and load, increases markedly after blotting mesothelial surface with filter paper;this increase is only partially reduced by wetting blotted mesothelium with Ringer solution. Given thatmesothelial surface is covered by a thick coat with sialomucin and hyaluronan, we tested whether additionof sialomucin or hyaluronan solution after blotting lowers more than Ringer alone. Actually, thesemacromolecules lowered more than Ringer, so that was no longer significantly higher than its preblottingvalue. Moreover, Ringer addition, after washout of macromolecule solution, increased , in linewith their dilution. These findings indicate that mesothelial blotting removes part of these moleculesfrom the coat covering mesothelial surface, and their relevance for pleural lubrication. Transmission electronmicrographs of pleural specimens after mesothelial blotting showed that microvilli were partiallyor largely removed from mesothelium, consistent with a substantial loss of macromolecules normallyentrapped among them.