Characteristics of normal rabbit pleural fluid: Physiologic and biochemical implications

Each normal rabbit pleural space contains approximately 0.2 ml of collectable, clear liquid. This fluid has a total cell count of 1503±414 cells/mm³, the majority of which are monocytic cells. Pleural fluid total protein concentration (1.4±0.1 gm/100 ml) is approximately 20%, and lactic dehydrogenase concentration (129±6 Wrobleski U/ml) is approximately 40% of that found in blood. Pleural fluid and blood glucose were equivalent, and venous serum chloride concentration was slightly higher than the simultaneously measured pleural fluid value. Normal rabbit pleural fluid is alkaline; the value of 7.66±0.02 probably is slightly higher than the actual pH value owing to the escape of CO₂. A 8–9 mEq/liter HCO ₃ ^? gradient was found between pleural fluid and venous blood. The HCO ₃ ^? gradient cannot be explained by the Gibbs-Donnan equilibrium, suggesting that a process of active transport, possibly chloride pumping, is involved.