Pleural fluid exchange in rabbits

The study was designed to better characterize pleural fluid absorption in rabbits with the following two objectives: to determine the relative absorption of saline versus high-protein solutions, and to identify the relative rates of absorption of dextran molecules of varying sizes.

Twenty New Zealand white rabbits received a 12-mL intrapleural injection of saline solution and a 10% protein solution on opposite sides, each solution containing dextran molecules with varying MWs. At sacrifice at 1, 4, 8, 18 and 24 h, the volume of pleural fluid and the concentrations of the dextran molecules were determined.

Saline was absorbed faster than the high-protein fluid (P < 0.001). Dextran concentrations in the saline were significantly higher than those in the protein solution at all times after injection (P = 0.005; P < 0.001, respectively). The higher-MW dextrans were cleared more slowly than the lower-MW dextrans in a continuously graded manner.

Saline was absorbed faster than a solution with a high protein content. There was a continuous spectrum in the rate of absorption of the dextran molecules, with the larger molecules being absorbed more slowly.