Terbutaline stimulates alveolar fluid resorption in hyperoxic lung injury JOSEPH M. LASNIER, O. DOUGLAS WANGENSTEEN, LAURA S. SCHMITZ, CYNTHIA R. GROSS, AND DAVID H. INGBAR Departments of Medicine, Physiology, Pathology and Nursing, Schools of Medicine and Pharmacy, University of Minnesota, Minneapolis, Minnesota 55455 Lasnier, Joseph M., O. Douglas Wangensteen, Laura S. Schmitz, Cynthia R. Gross, and David H. Ingbar. Terbutaline stimulates alveolar fluid resorption in hyperoxic lung injury. J. Appl. Physiol. 81(4): 1723–1729, 1996.— Alveolar fluid resorption occurs by active epithelial sodium transport and is accelerated by terbutaline in healthy lungs. We investigated the effect of terbutaline on the rate of alveolar fluid resorption from rat lungs injured by hyperoxia. Rats exposed to .95% O 2 for 60 h, sufficient to increase wet-to-dry lung weight and cause alveolar edema, were compared with air-breathing control rats. After anesthesia, the animals breathed 100% O 2 for 10 min through a tracheos- tomy. Ringer solution was instilled into the alveoli, and the steady-state rate of volume resorbed at 6 cmH 2 O pressure was measured via a pipette attached to the tracheostomy tubing. Ringer solution in some animals contained terbuta- line (10 23 M), ouabain (10 23 M), or both. Normoxic animals resorbed 49 6 6 μl · kg 21 · min 21 ; ouabain reduced this by 39%, whereas terbutaline increased the rate by 75%. The effect of terbutaline was blocked by ouabain. Hyperoxic animals ab- sorbed 78 6 9 μl·kg 21 · min 21 ; ouabain reduced this by 44%. Terbutaline increased the rate by a mean of 39 μl · kg 21 ·min 21 , similar to the absolute effect seen in the normoxic group, and this was blocked by ouabain. Terbutaline accelerates fluid resorption from both normal and injured rat lungs via its effects on active sodium transport. ouabain; active sodium transport; sodium-potassium adeno- sinetriphosphatase; pulmonary edema ALTHOUGH it previously was thought that sodium and fluid movement across the alveolar epithelium was entirely due to passive diffusion driven by hydrostatic and osmotic pressure gradients, there is now ample evidence that active sodium transport across the alveo- lar epithelium plays a key role in driving isotonic fluid resorption. Vectorial active sodium transport has been demonstrated in cultured type II cells in monolayers (5, 8), isolated perfused lungs (1, 5, 6, 8, 16), and whole animals (3, 11, 16, 20, 23). Furthermore, lungs from sheep and humans actively resorb fluid despite the absence of blood flow or ventilation (19, 20). Active trans- port in these models is stimulated by b-agonists (3, 5–9, 11, 16, 18) and adenosine 3 8,58-cyclic monophosphate (cAMP) analogues (5, 8), showing that it is possible to pharmacologi- cally accelerate clearance, at least in normal lungs. In these models, transport also is inhibited by amiloride (1, 4, 5, 9, 11, 23) and ouabain (1, 9, 11, 19, 20), consistent with the idea that both the apical sodium channel and basolateral Na 1 -K 1 -adenosinetriphosphatase (ATPase) are critical for active transepithelial transport. The effects of lung injury on net sodium and fluid resorption are less clear. In rats, injury due to acute (60 h of .95% O 2 ) or chronic (7 days of 85% O 2 ) hyperoxia increases Na 1 -K 1 -ATPase mRNA, protein, and activity (4, 14, 15, 25) as well as sodium-channel protein and activity (10). Upregulation of Na 1 -K 1 -ATPase also oc- curs in type II cells isolated from rats ventilated with high pressures for 25 min (26). Recent human data suggest that patients with lung injury who resorb fluid have a better prognosis (13). However, there is little published data demonstrating that active sodium trans- port, and thus net fluid resorption, can be accelerated pharmacologically in an injured lung (12, 22). Because acceleration of fluid clearance in lung injury may improve outcome, we have used a recently developed model to test the hypothesis that terbutaline will accelerate net fluid resorption in an injured lung. Hyperoxia was chosen as a method of inducing lung injury because the morphological changes associated with 60 h of 100% O 2 are well described (27) and include alveolar edema accompanied by increased wet-to-dry lung weight (14); in addition, increases in Na 1 -K 1 - ATPase mRNA and protein have been demonstrated in this model (4, 14). METHODS Fluid resorption measurement. Measurement of fluid resorp- tion was based on a model described by Vejlstrup et al. (28) in which fluid resorption was monitored by following the volume change in a calibrated system attached to a fluid-filled rabbit lung. In our experiments, male Sprague-Dawley specific pathogen-free rats (Harlan, Madison, WI), weight 175–250 g, were anesthetized with pentobarbital sodium (80 mg/kg ip), and a tracheostomy was performed. Inspired O 2 fraction of 1.0 was administered with 2–4 cmH 2 O constant positive airway pressure for 10 min to facilitate subsequent degassing of the lungs. Ringer solution that previously had been bubbled for 10 min with 100% O 2 was instilled via the tracheostomy; cardiac arrest occurred within a few minutes of instillation. The composition of the Ringer solution was as follows (in mM): 137 NaCl, 2.68 KCl, 1.25 MgSO 4 , 1.82 CaCl 2 , 5.55 glucose, and 12 N-2-hydroxyethylpiperazine-N8-2-ethanesul- fonic acid. The pH was adjusted to 7.4 and sufficient blue dextran (mol wt 2 3 10 6 ) was added to color the solution, with a resulting osmolality of 270–290 mosmol. The tracheostomy tubing was then attached to a graduated 1-ml fluid-filled pipette supported in a horizontal position at a height of 6 cm above the table top. Thoracotomy was performed to document adequate degassing and filling of the lungs with the Ringer solution. The temperature in the thorax was monitored and maintained at 37°C with a heating blanket placed below the animal. Volume measurements were taken every 10 min by following the meniscus in the pipette. These values were recorded through the initial equilibration period and for $40 min with a stable rate of clearance, as defined by interval measurements varying by no more than 25%. The volume 0161-7567/96 $5.00 Copyright r 1996 the American Physiological Society 1723 by 10.220.32.246 on April 5, 2017 http://jap.physiology.org/ Downloaded from