Alveolar epithelial barrier functions in ventilated perfused rabbit lungs

We employed ultrasonic nebulization for homogeneous alveolar tracer deposit ion into ventilated perfused rabbit lungs. Na-22 and I-125-albumin transit kinetics were monitored on-line with gamma detectors placed around the lung and the perfusate reservoir. [H-3] mannitol was measured by repetitive cou nting of perfusion fluid samples. Volume of the alveolar epithelial lining fluid was estimated with bronchoalveolar lavage with sodium-free isosmolar mannitol solutions. Sodium clearance rate was -2.2 +/- 0.3%/ min. This rate was significantly reduced by preadministration of ouabain/amiloride and en hanced by pretreatment with aerosolized terbutaline. The I-125-albumin clea rance rate was -0.40 +/- 0.05%/min. The appearance of [H-3] mannitol in the perfusate was not influenced by ouabain/amiloride or terbutaline but was m arkedly enhanced by pretreatment with aerosolized protamine. An epithelial lining fluid volume of 1.22 +/- 0.21 ml was calculated in control lungs. Fl uid absorption rate was 1.23 mul .g lung weight(-1). min(-1), which was blu nted after pretreatment with ouabain/amiloride. We conclude that alveolar t racer loading by aerosolization is a feasible technique to assess alveolar epithelial barrier properties in aerated lungs. Data on active and passive sodium flux, paracellular solute transit, and net fluid absorption correspo nd well to those in previous studies in fluid-filled lungs; however, albumi n clearance rates were markedly higher in the currently investigated aerate d lungs.