Time course of active and passive liquid and solute movement in the isolated perfused rat lung model

The isolated perfused rat lung model (IL) is used to study alveolar epithelial transport properties. Most of the previous studies have been done over a short period of time and have not used the same preparation as a control and intervention group. We evaluated whether the IL preparation could be used for a prolonged period of time (5 h) and studied the rates of active Na⁺ transport, lung liquid clearance, and passive movement of solutes. Active Na⁺ transport and lung liquid clearance were stable from 1 to 5 h. The passive movement of small solutes (Na⁺, mannitol) did not change significantly, and albumin movement increased slightly at the fifth hour. Total RNA isolated from IL after 5 h was intact, and the Na⁺-K⁺-ATPase activity in alveolar type II cells isolated at the end of 5-h experiments was equal to Na⁺-K⁺-ATPase function from freshly isolated alveolar type II cells. Finally, we measured the stimulatory effect of the β-adrenergic- agonist terbutaline and the inhibitory effect of the Na⁺-K⁺-ATPase- antagonist ouabain by using the same animal as a control. Accordingly, the isolated perfused lung model is functionally stable for at least 5 h, and it could be utilized to evaluate the effect of different interventions by using the same preparation.