Because the availability of transgenic mice makes it possible to examine the contribution of single genes to in vivo function, we developed a simple in situ mouse model that can be used to quantify isosmolar alveolar epithelial fluid clearance (AFC). Mice were killed, a tracheostomy was done, and then a test solution of a 5% isosmolar albumin solution with 0.1 μCi of125I-labeled albumin was instilled via the trachea into the distal air spaces of both lungs. After instillation, the lungs were inflated to 7 cmH2O with 100% O2 and maintained at 37°C by placing the animals under an infrared lamp. AFC was measured by the progressive increase in concentration of labeled and unlabeled protein over 1 h. The results indicated the following. 1) Basal, unstimulated AFC in mouse lungs was significantly faster than in ex vivo rat lungs (27 ± 5% in in situ mice vs. 11 ± 3% in ex vivo rat lungs; P < 0.05). 2) Comparison of equivalent doses (10−4 M) of β-adrenergic agonist (isoproterenol) and β2-adrenergic agonists (terbutaline and salmeterol) indicated that stimulated clearance occurred only in presence of isoproterenol. 3) Because atenolol, a specific β1-antagonist, abolished the effect of isoproterenol, the β-adrenergic stimulation appears to be mediated by β1-receptors. The rate of AFC in nonperfused mouse lungs was significantly faster than in prior studies of nonperfused lungs in rats and sheep. Interestingly, the stimulated clearance rate in mice was similar to the fast rates of AFC that we recently reported in patients recovering from hydrostatic pulmonary edema. This in situ model is a unique experimental preparation that can be readily used to quantify isosmolar epithelial fluid clearance in mice.
Changes in intracisternal peroxidase activity during alveolar epithelial differentiation in mouse lungs.
