The plasma-lymph exchange of two lactate dehydrogenase (LDH) isozymes (4.2 nM) of different molecular charge between plasma (CP) and lung lymph (CL), their initial clearances across the capillary wall, and their extravascular distribution volumes were studied in dog lungs at control and increased left atrial pressures (Pla = 23.3 +/- 2.1 cmH2O). The anionic LDH 1 [isoelectric point (pI) = 5.0] exhibited a more rapid plasma decay compared with cationic LDH 5 (pI = 7.9) after bolus injection but was maintained relatively constant in several experiments using a constant infusion. The mean 10- to 12-min lung tissue clearances were 40% higher for LDH 5 than LDH 1 at control Pla and 120% higher at increased Pla. The CL/CP ratios of the anionic LDH 1 were consistently higher at 4-5 h after simultaneous injection than those of cationic LDH 5. However, the extravascular distribution volumes of LDH 5 were significantly higher in lymph equivalents than those of LDH 1 at 4 h in both Pla groups. Fixed negative charges located on endothelial cells, basement membrane, and interstitial matrix could explain the observed differences between LDH isozymes in CL/CP ratios, tissue uptake, and extra-vascular distribution volumes by the ionic interaction of LDH 5 with these negative change sites which would retard the plasma-lymph transport and enhance the extravascular distribution volume and initial clearance of these cationic macromolecules.

The reabsorption of albumin from the pleural space was measured in eight dogs receiving 0.5 ml intrapleural injection of 131I-labeled albumin and a simultaneous intravenous injection of 125I-labeled albumin. Plasma curves for both tracers were obtained over 24 h. The 125I-albumin curve served as input function of albumin for interstitial spaces, including pleura, whereas the 131I-albumin curve represented the output function from pleural space. The frequency function of albumin transit times from pleural space to plasma was obtained by deconvolution of input-output plasma curves. Plasma recovery of 131I-albumin was complete by 24 h, and the mean transit time from pleura to plasma averaged 7.95 +/- 1.57 (SD) h. Albumin reabsorption occurred mainly via lymphatics as indicated by experiments in 16 additional dogs in which their right lymph ducts or thoracic ducts were ligated before intrapleural injection. A pleural lymph flow of 0.020 +/- 0.003 (SD) ml.kg-1.h-1 was estimated, which is balanced by a comparable filtration of fluid into the pleural space. This suggests that, under physiological conditions, the subpleural lymphatics represent an important control mechanism of pleural liquid pressure.

To determine whether the accelerated rate of lobe weight gain during severe pulmonary edema is attributed to increased permeability of the microvascular barrier or a loss of tissue forces opposing filtration, the effect of edema on capillary filtration coefficient (Kf,C), interstitial compliance (Ci), and the volume of fluid filtered after a step increase in microvascular pressure (delta Vi) were determined in eight isolated left lower lobes of dog lungs perfused at 37 degrees C with autologous blood. After attaining a base-line isogravimetric state, the capillary pressure (Pc) was increased in successive steps of 2, 5, and 10 cmH2O. This sequence of vascular pressure increases was repeated three times. Edema accumulation was expressed as weight gained as a percent of initial lobe weight (% delta Wt), and Kf,C was measured by time 0 extrapolation of the weight gain curve. An exponential rate constant for the decrease in the rate of weight gain with time (K) was calculated for each curve. Ci was then calculated by assuming that the capillary wall and interstitium constitute a resistance-capacitance network. Kf,C was not increased by edema formation in any group. Between mild (% delta Wt less than 30%) and severe edema states (% delta Wt greater than 50%) respective mean Ci increased significantly from 3.54 to 9.12 ml.cmH2O-1.100 g-1, K decreased from 0.089 to 0.036 min-1, and delta Vi increased from 1.28 to 2.4 ml.cmH2O-1.100 g-1. The delta Vi during each Pc increase was highly correlated with Kf,C and Ci when used together as independent variables (r = 0.99) but less well correlated when used separately.(ABSTRACT TRUNCATED AT 250 WORDS)