EFFECT OF TEMPERATURE ON ALVEOLAR LIQUID AND PROTEIN CLEARANCE IN AN IN-SITU PERFUSED GOAT LUNG

To study the mechanisms of alveolar liquid and protein clearance, we investigated the effect of four different temperatures (7, 18, 30, and 38-degrees-C) on the rate of liquid, [C-14]mannitol, and I-125-labeled albumin (I-125-albumin) transport from the air spaces of isolated perfused in situ goat lungs over 4 h under isogravimetric conditions. The concentrations of both native proteins and I-125-albumin in the alveolar fluid after 4 h were used to estimate alveolar liquid clearance. We instilled autologous serum (2 ml/kg) with I-125-albumin and [C-14]mannitol into the distal air spaces of one lung and I-131-labeled albumin into the perfusate to measure the capillary-to-alveolar permeability to protein. Alveolar liquid clearance progressively declined from a control value of 24 +/- 6% at 38-degrees-C to 12 +/- 7% at 30-degrees-C, to 3 +/- 3% at 18-degrees-C, and to -15 +/- 11% at 7-degrees-C. I-125-albumin clearance into the perfusate was 0.3%/h of the instilled I-125-albumin at 38-degrees-C. The clearance decreased abruptly to 0.06%/h at 30-degrees-C and then slightly increased to 0.08%/h at 18-degrees-C and to 0.15%/h at 7-degrees-C. There were no changes in transport except for a twofold increase in mannitol at 7-degrees-C. Increased permeability of the alveolar barrier to protein and small-molecular-weight tracers at 7-degrees-C indicates that the barrier function of the alveolar epithelium is disrupted at this low temperature. The inhibition of liquid clearance from the air spaces at 18 and 30-degrees-C provides further support for the importance of active mechanisms for removal of excess alveolar liquid. The decline in alveolar protein clearance without change in mannitol clearance at 18 and 30-degrees-C is consistent with temperature-dependent mechanisms for some of the protein clearance from the air spaces.