Fluid Clearance In Rats Research Articles

Effects of dexmedetomidine on alveolar fluid clearance in rats with acute lung injury induced by lipopolysaccharide

Objective To investigate effects of dexmedetomidine(Dex) on alveolar fluid clearance (AFC) in rats with acute lung injury induced by lipopolysaccharide (LPS). Methods Forty-eight male Wistar rats were randomly divided into normal saline control (NS) group, LPS group, and Dex treatment (LPS+Dex) group. The rats in NS group were intravenously injected with 0.9% normal saline (5 ml/kg) followed by influsion of 0.9% normal saline (5 μg·kg-1·h-1). The rats in LPS group were intravenously injected with LPS (10 mg/kg) followed by influsion of 0.9% normal saline (5 μg·kg-1·h-1). The rats in LPS+Dex group were intravenously injected with LPS (10 mg/kg) followed by influsion of Dex (5 μg·kg-1·h-1). The rats were sacrificed 6 h after intravenous injection of LPS or NS, PaO2 was measured, AFC was determined by Evans blue-tagged albumin concentration changes. Histology of the lungs were assayed with H-E staining. The wet/dry weight ratio (W/D) of the lung was determined. The levels of TNF-α and IL-1β in the lung tissues were assessed by ELISA. The protein levels of potassium sodium adenosine triphosphate enzyme (Na-K-ATPase), alveolar epithelial sodium channel (ENaC) were detected by Western blot and immunohistochemistry. Results Compared with NS group, PaO2 was lower in LPS group, and this drop was reversed by Dex (in LPS+Dex group)(P<0.01). The W/D and the concentrations of TNF-α and IL-1β in the pulmonary tissues were increased in the LPS group, relative to the NS group, but the increases were compromised in the LPS+Dex group(P<0.01). AFC was reduced in LPS group, relative to NS group, but the reduction was compensat in LPS+Dex group(P<0.01). The expression of Na-K-ATPase and ENaC was lower in the LPS group than the NS group, but they were normalized in the LPS+Dex group(P<0.01). Conclusions Our findings suggest that dexmedetomidine may alleviate pulmonary edema by increasing AFC and the expression of Na-K-ATPase and ENaC in rats with acute lung injury induced by lipopolysaccharide. Key words: Dexmedetomidine; Acute lung injury; Alveolar fluid clearance; Potassium sodium adenosine triphosphate enzyme; Alveolar epithelial sodium channel

Protectin DX increases alveolar fluid clearance in rats with lipopolysaccharide-induced acute lung injury

Acute respiratory distress syndrome is a life-threatening critical syndrome resulting largely from the accumulation of and the inability to clear pulmonary edema. Protectin DX, an endogenously produced lipid mediator, is believed to exert anti-inflammatory and pro-resolution effects. Protectin DX (5 µg/kg) was injected i.v. 8 h after LPS (14 mg/kg) administration, and alveolar fluid clearance was measured in live rats (n = 8). In primary rat ATII epithelial cells, protectin DX (3.605 × 10−3 mg/l) was added to the culture medium with LPS for 6 h. Protectin DX improved alveolar fluid clearance (9.65 ± 1.60 vs. 15.85 ± 1.49, p < 0.0001) and decreased pulmonary edema and lung injury in LPS-induced lung injury in rats. Protectin DX markedly regulated alveolar fluid clearance by upregulating sodium channel and Na, K-ATPase protein expression levels in vivo and in vitro. Protectin DX also increased the activity of Na, K-ATPase and upregulated P-Akt via inhibiting Nedd4–2 in vivo. In addition, protectin DX enhanced the subcellular distribution of sodium channels and Na, K-ATPase, which were specifically localized to the apical and basal membranes of primary rat ATII cells. Furthermore, BOC-2, Rp-cAMP, and LY294002 blocked the increased alveolar fluid clearance in response to protectin DX. Protectin DX stimulates alveolar fluid clearance through a mechanism partly dependent on alveolar epithelial sodium channel and Na, K-ATPase activation via the ALX/PI3K/Nedd4–2 signaling pathway.

The Role of Angiotensin II and Cyclic AMP in Alveolar Active Sodium Transport.

Active alveolar fluid clearance is important in keeping airspaces free of edema. Angiotensin II plays a role in the pathogenesis of hypertension, heart failure and others. However, little is known about its contribution to alveolar fluid clearance. Angiotensin II effects are mediated by two specific receptors; AT1 and AT2. The localization of these two receptors in the lung, specifically in alveolar epithelial cells type II, was recently reported. We hypothesize that Angiotensin II may have a role in the regulation of alveolar fluid clearance. We investigated the effect of Angiotensin II on alveolar fluid clearance in rats using the isolated perfused lung model and isolated rat alveolar epithelial cells. The rate of alveolar fluid clearance in control rats was 8.6% ± 0.1 clearance of the initial volume and decreased by 22.5%, 28.6%, 41.6%, 48.7% and 39% in rats treated with 10-10 M, 10-9 M, 10-8 M, 10-7 M or 10-6 M of Ang II respectively (P < 0.003). The inhibitory effect of Angiotensin II was restored in losartan, an AT1 specific antagonist, pretreated rats, indicating an AT1 mediated effect of Ang II on alveolar fluid clearance. The expression of Na,K-ATPase proteins and cAMP levels in alveolar epithelial cells were down-regulated following the administration of Angiotensin II; suggesting that cAMP may be involved in AngII-induced reduced Na,K-ATPase expression, though the contribution of additional factors could not be excluded. We herein suggest a novel mechanism of clinical relevance by which angiotensin adversely impairs the ability of the lungs to clear edema.

The role of amiloride‐insensitive sodium transport in alveolar fluid homeostasis (695.2)

Under both normal and pathological conditions, the lung fluid balance across the alveolar epithelial barrier is mainly regulated by active sodium transporters. Previous work has largely focused on the critical role of ENaC, yet ~60% of alveolar fluid clearance in rats or humans is amiloride insensitive. We decided to explore the role of the amiloride‐insensitive sodium cotransporters SGLT1 (Na+‐glucose co‐transporter 1) and SNATs (Na+‐coupled neutral amino acid transporters) in the intact lung. In isolated perfused rat lungs, we determined alveolar fluid clearance (AFC) using a double indicator dilution technique and probed for the role of SGLT1 and SNATs by addition of appropriate cotransporter substrates or inhibitors. While addition of the SNAT substrate L‐alanine did not affect basal AFC, it rescued AFC in lungs pre‐treated with amiloride, and this response was blocked by the SNAT inhibitor HgCl2. Analysis of bronchoalveolar lavage fluid revealed &gt; 2‐fold of L‐alanine in the epithelial lining fluid compared to plasma level. RT‐PCR identified mRNAs for all 6 SNAT isoforms in whole lung, yet in alveolar epithelial cells, only SNAT 2 and 5 mRNA and protein were detected. In contrast, no functional involvement of SGLT1 in AFC was detected. These results indicate a new role for SNATs in AFC which becomes unmasked when ENaC is inhibited. SNAT2 and SNAT5 may represent novel targets for the resolution of pulmonary edema.Grant Funding Source: Funded by CIHR MOP # 245251

The Effect of Endogenous Angiotensin II on Alveolar Fluid Clearance in Rats with Acute Lung Injury

In acute lung injury (ALI), angiotensin II (Ang II) plays a vital role in the stimulation of pulmonary permeability edema formation through the angiotensin type 1 (AT1) receptor. The effect of Ang II on alveolar fluid clearance (AFC) in ALI remains unknown. Sprague Dawley rats were anesthetized and intratracheally injected with 1 mg⁄kg lipopolysaccharide (LPS), while control rats received saline. The AT1 receptor antagonist ZD7155 was injected intraperitoneally (10 mg⁄kg) 30 min before LPS administration. The lungs were isolated for AFC measurement, and alpha-epithelial sodium channel (ENaC) messenger RNA and protein expression were detected by reverse-transcription polymerase chain reaction and Western blot. LPS-induced ALI caused an increase in Ang II levels in plasma and lung tissue but a decrease in AFC. The time course of Ang II levels paralleled that of AFC. Pretreatment with ZD7155 prevented ALI-induced reduction of AFC. ZD7155 also reversed the ALI-induced reduction of beta-ENaC and gamma-ENaC levels, and further decreased alpha-ENaC levels. These findings suggest that endogenous Ang II inhibits AFC and dysregulates ENaC expression via AT1 receptors, which contribute to alveolar filling and pulmonary edema in LPS-induced ALI.

Endogenous catecholamine stimulates alveolar fluid clearance in rats with acute pancreatitis

Acute pancreatitis causes pulmonary oedema with the accumulation of fluid in the alveolar spaces, possibly due to reduced clearance. This study tested the hypothesis that acute pancreatitis decreases alveolar fluid clearance in a rat model of pulmonary oedema during acute pancreatitis. Acute pancreatitis was induced by a retrograde injection of 5% taurocholate sodium (0.2 mL) into the common bile duct. The lungs were isolated 4, 24 and 48 h after the induction of acute pancreatitis and alveolar fluid clearance was measured in the absence of pulmonary perfusion. Alveolar fluid clearance increased to 31.0 +/- 3.5% of instilled volume/h in rats with acute pancreatitis for 4 h compared with 17.3 +/- 1.0% of instilled volume/h in sham rats (P < 0.01), then returned to the control level 48 h after acute pancreatitis (16.0 +/- 4.1% of instilled volume/h). In contrast, the lung water to dry lung weight ratio decreased maximally 24 h after acute pancreatitis (P < 0.01), then returned to the control level 48 h after acute pancreatitis. The plasma epinephrine levels increased to 25-fold higher in rats with acute pancreatitis for 4 h than in sham rats without acute pancreatitis. Prazosin (an alpha(1)-adrenergic antagonist, 10(-4) mol/L), yohimbine (an alpha(2)-adrenergic antagonist, 10(-4) mol/L) or a bilateral adrenalectomy inhibited the increase in part, a combination of prazosin (10(-4) mol/L) and yohimbine (10(-4) mol/L) completely inhibited the increase in alveolar fluid clearance in rats after acute pancreatitis for 4 h, whereas propranolol (a beta-adrenergic antagonist, 10(-4) mol/L) had no effect. Endogenous catecholamine stimulates alpha-adrenoceptors and increases alveolar fluid clearance in rats with acute pancreatitis.

Chronic pulmonary artery occlusion increases alveolar fluid clearance in rats

We had observed that pulmonary artery ligation for 14 days did not induce lung infiltration in a patient who had undergone a lobectomy for lung cancer. Our hypothesis was that long-term pulmonary artery ligation decreased lung water volume and/or increased alveolar fluid clearance. We determined the mechanism responsible for lung water balance in rats with chronic pulmonary artery occlusion for 14 days. Sprague-Dawley rats (n = 45) were used. Through a left thoracotomy, the left pulmonary artery was ligated for 14 days. Then, we measured lung water volume, alveolar fluid clearance, the effects of beta-adrenergic agonist and antagonist, mRNA expression, and protein expression in the lungs. Chronic left pulmonary artery occlusion increased both lung water volume and alveolar fluid clearance in the left lungs, but not in the right lungs with pulmonary perfusion. Neither a beta-agonist nor a beta-antagonist changed the increase in alveolar fluid clearance. Real-time polymerase chain reaction revealed an increase in alpha1-Na,K-ATPase mRNA and a decrease of beta2-adrenoreceptor mRNA, but no change in beta1-Na,K-ATPase mRNA and alpha-, beta-, gamma-epithelial sodium channel mRNA, in the left lung without pulmonary perfusion. Western blot analysis revealed an increase in alpha1-Na,K-ATPase subunit, but no change in beta1-Na,K-ATPase subunit. Chronic pulmonary artery occlusion increases alveolar fluid clearance via alpha1-Na,K-ATPase overexpression in rats.

Malnutrition causes a reduction in alveolar epithelial sodium and chloride transport which predisposes to death from lung injury

All forms of malnutrition have been associated with increased severity of pneumonia, an increased pneumonia associated mortality and an increased risk of pulmonary fluid overload. Malnutrition was found to be associated with increased sweat sodium and chloride concentrations. A reduction of systemic sodium and chloride transport reflected in sweat sodium and chloride levels has been linked to increased severity of pulmonary edema in children with septicemia. Malnutrition causes a reduction in alveolar epithelial sodium and chloride transport which predisposes to death from lung injury. SUPPORTING EVIDENCE FOR THE HYPOTHESIS: Malnutrition caused reduced pulmonary fluid clearance in the rat model. Amiloride insensitive pulmonary fluid clearance in malnourished rats was reduced. The reduction in fluid clearance was reversible by beta agonists which increases epithelial sodium and chloride transport. Reduction of alveolar ion and fluid transport capacity explains the predisposition to death from pulmonary edema associated with intravenous fluids and blood transfusions in inpatients with malnutrition. Reduced alveolar epithelial ion transport impairs absorption of intra-alveolar inflammatory exudate in pneumonia leading to a increased severity of respiratory compromise and increased mortality. MEANS TO TEST THE HYPOTHESIS: Nasal potential difference measurements could compare airway epithelial sodium and chloride transport in patients with and without malnutrition and malnutrition associated lung disease. Sweat sodium and chloride concentrations could be compared in patients with and without respiratory disease associated with malnutrition and correlated with the severity of respiratory compromise.

Increased amiloride insensitive alveolar fluid clearance in rats with severe congestive heart failure

Epithelial sodium channels (ENaC) play a central role in alveolar fluid clearance (AFC). We have previously shown that rats with severe congestive heart failure (CHF) have increased protein levels of the αENaC subunit, whereas the βENaC subunit is almost absent, suggesting predominance of the less efficient nonselective cation channel type in alveolar cells in severe CHF. The present study examined whether severe CHF was associated with quantitative changes in AFC. CHF was induced in male Wistar rats by LAD-ligation. Sham operated rats were used as controls. Rats were examined 3-5 weeks after LAD/Sham ligation. CHF had left ventricular end diastolic pressure > 15 mmHg and were postmortally devided into two groups based on right ventricular mass (RVM): Moderate CHF: RVM: 0.21±0.01g; Severe CHF: RVM: 0.37±0.04 g. RVM in Sham-operated controls: 0.16±0.01 g. AFC over 60 minutes was measured by installation of I125-Albumin in 5 % BSA in Ringer lactate into the lungs in ventilated anesthetized rats. The final to installed protein concentration ratio was significantly increased in severe CHF rats (1.27±0.03) and unchanged in moderate CHF rats (1.10±0.02) when compared to controls (1.10±0.01). AFC was completely inhibited with amiloride in both control rats (1.01±0.01) and rats with moderate CHF (1.01±0.05), but could not be inhibited in rats with severe CHF (1.24±0.06). The results indicate that rats with severe CHF have increased amiloride insensitive AFC, suggesting activation of alternative sodium transport pathways contributing to AFC in severe CHF. The study received financial support from the Danish Heart Foundation.

Effect of beta-adrenergic agonist on alveolar fluid clearance in rats

Effect of beta-adrenergic agonist on alveolar fluid clearance in rats

Effect of beta-adrenergic agonist on alveolar fluid clearance in rats with acute lung injury

Effect of beta-adrenergic agonist on alveolar fluid clearance in rats with acute lung injury

A prostacyclin analogue, OP-41483alpha-CD, restores the ability of a beta2-adrenergic agonist to stimulate alveolar fluid clearance in rats.

It is not yet known whether a prostacyclin analogue can affect alveolar fluid clearance. According to recent studies, high-dose (10(-3) M) terbutaline, a beta(2)-adrenergic agonist, failed to increase alveolar fluid clearance. Therefore, we examined the effects of OP-41483alpha-CD, a prostacyclin analogue, on alveolar fluid clearance in the presence of high-dose terbutaline in rats. Albumin solution containing Evans blue dye and various drugs was instilled into the alveolar airspaces of isolated rat lungs, which were then inflated with 100% oxygen at an airway pressure of 8 cmH(2)O. Alveolar fluid clearance was measured by the progressive increase in dye concentrations over 1 h. Although 10(-5) and 10(-4) M terbutaline increased alveolar fluid clearance, 10(-3) M terbutaline did not. OP-41483alpha-CD restored the ability of 10(-3) M terbutaline to stimulate alveolar fluid clearance. The effect of OP-41483alpha-CD was consistent with the effect of atenolol, a beta(1)-adrenergic antagonist. The effect of OP-41483alpha-CD on alveolar fluid clearance was unchanged in lungs inflated with nitrogen. Prostaglandin E (PGE)(1) and PGE(2) analogues had similar effects to OP-41483alpha-CD on alveolar fluid clearance. These results indicate that a prostacyclin analogue restores the ability of high-dose terbutaline to stimulate alveolar fluid clearance.

Malnutrition impairs alveolar fluid clearance in rat lungs.

Inadequate nutrition complicates the clinical course of critically ill patients, and many of these patients develop pulmonary edema. However, little is known about the effect of malnutrition on the mechanisms that resolve alveolar edema. Therefore, we studied the mechanisms responsible for the decrease in alveolar fluid clearance in rats exposed to malnutrition. Rats were allowed access to water, but not to food, for 120 h. Then, the left and right lungs were isolated for the measurement of lung water volume and alveolar fluid clearance, respectively. The rate of alveolar fluid clearance was measured by the progressive increase in the concentration of Evans blue dye that was instilled into the distal air spaces with an isosmolar 5% albumin solution over 1 h. Malnutrition decreased alveolar fluid clearance by 38% compared with controls. Amiloride (10(-3) M) abolished alveolar fluid clearance in malnourished rats. Either refeeding for 120 h following nutritional deprivation for 120 h or an oral supply of sodium glutamate during nutritional deprivation for 120 h restored alveolar fluid clearance to 91 and 86% of normal, respectively. Dibutyryl-cGMP, a cyclic nucleotide-gated cation channel agonist, increased alveolar fluid clearance in malnourished rats supplied with sodium glutamate. Terbutaline, a beta(2)-adrenergic agonist, increased alveolar fluid clearance in rats under all conditions (control, malnutrition, refeeding, and glutamate-treated). These results indicate that malnutrition impairs primarily amiloride-insensitive and dibutyryl-cGMP-sensitive alveolar fluid clearance, but this effect is partially reversible by refeeding, treatment with sodium glutamate, or beta-adrenergic agonist therapy.

Lidocaine induces a reversible decrease in alveolar epithelial fluid clearance in rats.

Lidocaine is widely used in patients with acute cardiac disorders and has also been recently implicated as a possible cause of pulmonary edema after liposuction. The objective of this study was to assess the effect of lidocaine on alveolar fluid clearance, the primary mechanism responsible for the resolution of alveolar edema. Alveolar fluid clearance was measured in 29 ventilated rats using our well-validated method over 1 h using a 5% albumin solution instilled into the distal air spaces of the lung. Lidocaine was added to the instilled albumin solution (10(-5) M) or administered intravenously at a dose estimated to achieve a clinically relevant plasma concentration of 10(-5) M. Standard agonists and antagonists were used to determine the effect of lidocaine on alveolar fluid clearance. To determine whether lidocaine acted predominantly on the apical or basal surface, we also used QX314, lidocaine n-ethyl bromide quaternary salt, an analog of lidocaine, which is unable to cross the alveolar epithelium. The effect of lidocaine on the apical epithelial sodium channel transfected in Xenopus oocytes was also studied. Alveolar or intravenous lidocaine decreased alveolar fluid clearance by 50%, an effect that was reversible with the beta2 agonist, terbutaline. Lidocaine acted predominantly on the basal surface of the epithelium because n-ethyl bromide quaternary salt decreased alveolar fluid clearance only when it was given intravenously and because lidocaine did not inhibit the apical epithelial sodium channel when expressed in oocytes. Lidocaine decreased alveolar fluid clearance by 50%, an effect that may have major clinical implications in the care of patients with cardiac disease or during the perioperative period in some patients. Importantly, the effect of lidocaine was completely reversible with beta2-adrenergic therapy.

Beta1-Adrenergic Agonist Is a Potent Stimulator of Alveolar Fluid Clearance in Hyperoxic Rat Lungs

Because it was still uncertain whether a stimulation of β1-adrenoceptors accelerated alveolar fluid clearance in hyperoxic lung injury, the effect of denopamine, a selective β1-adrenergic agonist, on alveolar fluid clearance was determined in rats exposed to 93% oxygen for 48 and 56 h. Alveolar fluid clearance was measured by the progressive increase in the concentration of Evans blue labeled albumin instilled into the alveolar spaces over 1 h at 37°C in isolated rat lungs. The principle results were as follows: 1) Although lung water volume increased in rats exposed to hyperoxia for 48 and 56 h, basal alveolar fluid clearance did not change for up to 56 h; 2) Denopamine increased alveolar fluid clearance in rats exposed to hyperoxia as well as in rats without exposure to hyperoxia; 3) Denopamine primarily increased amiloride-insensitive alveolar fluid clearance in rats exposed to hyperoxia; 4) The potency of denopmaine was similar to that of terbutaline, a selective β2-adrenergic agonist. In summary, denopamine is a potent stimulator of alveolar fluid clearance in rats exposed to hyperoxia.

MODULATION OF TRANSALVEOLAR FLUID ABSORPTION BY ENDOGENOUS ALDOSTERONE IN ADULT RATS

We examined whether transalveolar fluid transport is modulated by aldosterone in adult rats. Because colocalization of mineralocorticoid receptors (MR) with 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) is important for aldosterone specific action, we first determined the immunohistochemical distribution of MR and 11betaHSD2 in the lung. We found that alveolar epithelial cells express both MR and 11betaHSD2. Reverse transcriptase polymerase chain reaction (RT-PCR) demonstrated that rat alveolar type II epithelial cells express both MR and 11betaHSD2. We then measured alveolar fluid clearance in rats treated with chronic low-sodium diet. A low-sodium diet (0.1% NaCl for 12 to 14 days) caused hyperaldosteronism accompanied by hypokalemia, whereas serum corticosterone and adrenaline levels remained normal. We found that hyperaldosteronism was associated with significantly higher alveolar fluid clearance and that this increase was related to the amiloride-sensitive component. In addition, the increase in alveolar fluid clearance was inhibited by spironolactone. Our results show that aldosterone is able to stimulate Na+ channels of alveolar epithelial cells. We conclude that alveolar epithelium is a physiological target tissue for aldosterone and transalveolar fluid absorption could in part be modulated by endogenous aldosterone acting via MR.

Beta-adrenergic agonist therapy accelerates the resolution of hydrostatic pulmonary edema in sheep and rats.

To determine whether beta-adrenergic agonist therapy increases alveolar liquid clearance during the resolution phase of hydrostatic pulmonary edema, we studied alveolar and lung liquid clearance in two animal models of hydrostatic pulmonary edema. Hydrostatic pulmonary edema was induced in sheep by acutely elevating left atrial pressure to 25 cmH(2)O and instilling 6 ml/kg body wt isotonic 5% albumin (prepared from bovine albumin) in normal saline into the distal air spaces of each lung. After 1 h, sheep were treated with a nebulized beta-agonist (salmeterol) or nebulized saline (controls), and left atrial pressure was then returned to normal. beta-Agonist therapy resulted in a 60% increase in alveolar liquid clearance over 3 h (P < 0.001). Because the rate of alveolar fluid clearance in rats is closer to human rates, we studied beta-agonist therapy in rats, with hydrostatic pulmonary edema induced by volume overload (40% body wt infusion of Ringer lactate). beta-Agonist therapy resulted in a significant decrease in excess lung water (P < 0.01) and significant improvement in arterial blood gases by 2 h (P < 0.03). These preclinical experimental studies support the need for controlled clinical trials to determine whether beta-adrenergic agonist therapy would be of value in accelerating the resolution of hydrostatic pulmonary edema in patients.

Halothane and isoflurane decrease alveolar epithelial fluid clearance in rats.

Active sodium transport is the primary mechanism that drives alveolar fluid clearance. In the current study, the effects of exposure to halothane and isoflurane on alveolar fluid clearance in rats were evaluated. Rats were exposed to either halothane (0.4% for 6 h or 2% for 2 h) or isoflurane (0.6% for 6 h or 2.8% for 2 h). Reversibility of halothane effects was assessed after 2 h of exposure to 2% halothane. Alveolar and lung liquid clearance were measured by intratracheal instillation of a 5% albumin solution with 1.5 microCi of 125I-albumin, during mechanical ventilation with 100% FiO2 and the halogenated agent. The effect of terbutaline (10(-4) M) added to the albumin solution was tested after 2 h of exposure to 2% halothane. The increase in protein concentration in the airspaces over 1 h was used to evaluate alveolar liquid clearance. Lung liquid clearance was calculated gravimetrically. Alveolar liquid clearance rates were decreased by 24%, 30% and 40% compared with controls (P < 0.05) after 2 h of exposure to halothane, 6 h of exposure to halothane, and 6 h of exposure to isoflurane, respectively. After 2 h of exposure to isoflurane, alveolar liquid clearance did not change. In the 2-h halothane exposure group, alveolar liquid clearance returned to the control value 2 h after withdrawal of halothane. Terbutaline increased alveolar liquid clearance by 50% and 89% in the control and 2-h halothane exposure groups, respectively. In all experiments, the same results were obtained for alveolar and lung liquid clearance. Halothane and isoflurane caused a reversible decrease in alveolar epithelial fluid clearance. Two hours of exposure to halothane did not alter the stimulatory effect of terbutaline on alveolar liquid clearance.