Solute-coupled liquid absorption from the pleural space

The occurrence of a solute-coupled absorption of liquid from the pleural space was studied by measuring in anesthetized rabbits the volume of liquid of the right pleural space 1 h after injecting into it 2 ml of Ringer solution or of Ringer with an inhibitor of a Na(+)-Cl- coupled transport or of the Na+/K+ pump. Volume collected after Ringer was 1.56 +/- 0.08 ml. Initial volume being 2.2 ml, net absorption rate was 0.64 ml/h. Volume collected after disulfonic stilbene (0.1 mM) or bumetanide (0.1 mM) was 2.01 +/- 0.06 and 2.01 +/- 0.05 ml, respectively; net absorption rate was reduced to 0.19 ml/h. This suggests the occurrence of Na(+)-Cl- coupled transports. Volume collected after ouabain (0.5 mM) was 2.08 +/- 0.08 ml; net absorption rate was reduced to 0.12 ml/h. This suggests the occurrence of the Na+/K+ pump. The marked reduction in the hydrothorax absorption produced by the inhibitors shows the occurrence of a solute-coupled liquid absorption from the pleural space. Liquid absorbed through the visceral pleura by the solute-coupled transport should be removed by the Starling forces of pulmonary capillaries. Solute-coupled absorption of liquid through the parietal pleura should oppose the filtration caused by the Starling forces.