Washout of protein in dog lung lymph

After an increase in microvascular filtration rate, lung lymph may contain protein washed from the tissue spaces plus protein from the filtrate. If so, then the lymphatic protein concentration may be significantly higher than the filtrate protein concentration (Cf). To test this hypothesis, we decreased the plasma protein concentration from 5.1 +/- 0.6 to 0.54 +/- 0.15 g/dl and increased the pulmonary microvascular filtration rate in four dogs. We estimated Cf to be 0.16 +/- 0.05 g/dl after we reduced the plasma protein concentration, and the lymphatic protein concentration (0.43 +/- 0.04 g/dl) was significantly greater than Cf. Our results indicate that lung microvascular membrane reflection coefficients estimated from lung lymph data may be too low. However, the amount of error caused by tissue protein washout is probably small. To account for the protein washout error, we estimated the lung microvascular membrane reflection coefficient to be approximately 0.74-0.76 instead of the approximately 0.70 previously reported for dogs (J. C. Gabel et al. J. Appl. Physiol. 55: 866-869, 1983).