To determine whether liquid and protein clearance from the air spaces and lungs of anesthetized and unanesthetized dogs is the same as in sheep, we quantified these variables at three different time periods (4, 8, and 12 h) by instilling heparinized plasma (3 ml/kg) labeled with 125I-albumin into one lower lobe. Protein clearance, measured from the residual 125I-albumin in the lung homogenate, was slow and monoexponential (approximately 1%/h), similar to our previous data for protein clearance from the lungs in sheep. Lung liquid clearance in dogs, however, was 50% less than in previous experiments in sheep. Residual lung liquid (as percent of instilled) was 88.7 +/- 7.0 at 4 h, 70.5 +/- 9.1 at 8 h, and 64.0 +/- 5.8 at 12 h. At each time period, alveolar protein concentration increased by 0.6 +/- 0.4 g/dl at 4 h, 1.3 +/- 1.2 g/dl at 8 h, and 2.1 +/- 0.8 g/dl at 12 h. This increase in alveolar protein concentration was proportional to the volume of liquid removed from the lungs. beta-Adrenergic agonist therapy with terbutaline (10(-5) M mixed with the instilled plasma) doubled the volume of liquid cleared from the lungs over 4 h, and the alveolar protein concentration increased proportionally. However, lung liquid clearance in dogs that were treated with beta-agonists was proportionally (50%) less than in sheep treated with beta-agonists. The slower liquid clearance in dogs compared with sheep cannot be explained by differences in hemodynamics, pulmonary blood flow, anesthesia, mode of ventilation, or alveolar surface area.(ABSTRACT TRUNCATED AT 250 WORDS)