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.