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Am. J. Respir. Crit. Care Med., Volume 156, Number 2, August 1997, 438-444

Dobutamine Increases Alveolar Liquid Clearance in Ventilated Rats by Beta-2 Receptor Stimulation

FRED A. TIBAYAN, ASHA N. CHESNUTT, HANS G. FOLKESSON, JON EANDI, and MICHAEL A. MATTHAY

Cardiovascular Research Institute, University of California, San Francisco

    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Although it is well known that beta-adrenergic agonist stimulation increases alveolar epithelial sodium and fluid transport, it is not known whether the beta-1 or the beta-2 receptor mediates this effect. Two clinically relevant beta-adrenergic agonists, dopamine (beta-1 agonist) and dobutamine (beta-1 and beta-2 agonist) were used to define the contribution of these two beta-receptors to beta-adrenergic stimulated fluid clearance from the air spaces of the lungs. Alveolar fluid clearance was measured in anesthetized, ventilated rats over one hour after instilling an isosmolar 5% albumin solution in Ringer's lactate with 3 µCi 125I-albumin. The concentrations of the labeled and unlabeled albumin were used to quantify alveolar liquid clearance. Dopamine, whether given intra-alveolar (10-4 M) or intravenously (5-10 µg/kg/min), had no effect. However, both intra-alveolar (10-4 M) and intravenous (5 µg/kg/min) dobutamine increased alveolar liquid clearance by approximately 50% over one hour compared to controls. ICI 118,551, a potent and specific beta-2 antagonist, blocked the effect of dobutamine. The dobutamine effect was blocked by amiloride (10-3 M), an inhibitor of sodium uptake. In summary, the beta-2 receptor mediates beta-adrenergic stimulation of alveolar epithelial sodium and fluid transport.

    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Numerous studies have established that alveolar liquid clearance can be stimulated by endogenous and exogenous beta-adrenergic agonists under normal and pathological conditions in several animal species (1). Recent evidence indicates that beta-adrenergic agonists increase alveolar liquid clearance in the resected human lung (6). However, it is not known whether this effect is mediated by the beta-1 or the beta-2 receptor; both of these receptors are present in the alveolar epithelium (7, 8).

Dobutamine and dopamine are vasoactive agonists that are used for a variety of clinical indications in patients with a low cardiac output and systemic hypotension. In clinically relevant doses, dobutamine has both beta-1 and beta-2 effects, but dopamine has only beta-1 effects, except at extremely high doses when dopamine may have some beta-2 effects as well (9, 10).

Therefore, the first objective of these studies was to determine the effect of dopamine and dobutamine on alveolar liquid clearance in anesthetized, ventilated rats. Both intra-alveolar and intravenous dopamine had an effect on alveolar liquid clearance. However, both intra-alveolar and intravenous dobutamine markedly increased alveolar liquid clearance. Therefore, the second objective was to define the mechanism for the dobutamine effect by using a specific beta-2 receptor inhibitor, ICI 118,551, to block the dobutamine effect and by measuring plasma epinephrine levels (to exclude a possible effect via endogenous release of epinephrine). While the one hour experiments provide definitive data on alveolar liquid clearance, the third objective was to carry out longer experiments (two hours) to examine quantitatively the effect of dobutamine on removal of excess fluid from the whole lung.

    METHODS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Surgical Preparation and Ventilation

Male Sprague Dawley rats (300-350 g; Simonsen, Gilroy, CA) were injected with sodium pentobarbital (50 mg/kg intraperitoneally, Nembutal®; Abbott Laboratories, Chicago, IL). A tracheostomy using a 2 mm ID endotracheal tube (PE-240, Clay Adams; Becton Dickinson and Company, Parsippany, NJ) was carried out and the lungs were mechanically ventilated with a constant-volume piston pump (Harvard Apparatus Co., Dover, MA) with an FIO2 of 1.0, peak airway pressure of 8-12 cm H2O, and positive end-expiratory pressure of 2-3 cm H2O. Respiratory rate was adjusted to maintain the arterial PCO2 between 27 and 35 mm Hg with a tidal volume of 10 ml/kg. A carotid arterial catheter (Clay Adams; Becton Dickinson and Company) was inserted to monitor systemic blood pressure and to sample arterial blood. A catheter was inserted into the jugular vein to administer either dopamine or dobutamine. Pancuronium bromide (0.3 mg /kg body weight, Pavulon®; Organon Inc., West Orange, NJ) was given intravenously for neuromuscular blockade. Body temperature was kept constant with a thermostatically controlled pad. For the experiments to measure left atrial pressure, the chest was opened with a median sternotomy and a catheter was inserted directly into the left atrium.

Preparation of Instillate

The instillate consisted of 5 g /100 ml bovine serum albumin (Sigma Chemical Co., St. Louis, MO) with Ringer's lactate that was prepared to be isosmolar with plasma. Evans blue (0.5 mg; Aldrich, Milwaukee, WI) was added to confirm the location of the aspirate at the end of the study. Three µCi of 125I-albumin (Merck-Frosst, Montreal, Canada) were added to the instillate as an alveolar protein tracer. Dobutamine (Gensia Laboratories, Irvine, CA), dopamine (SoloPak®; SoloPak Laboratories, Inc., Elk Grove Village, IL), amiloride (Sigma), or ICI 118,551 (Research Biochemicals International, Natick, MA) was added to the instillate in selected studies, as described below.

General Protocol

One hour experiments. A baseline of 30 min of stable systemic blood pressure was required before alveolar liquid instillation. As a vascular tracer protein, 131I-albumin (3 µCi; Merck-Frosst) was injected via the arterial catheter. Blood samples were taken every 15 min of the baseline period for arterial blood gases and radioactivity measurements. One milliliter of instillate was delivered into the right lung over 20-25 min by gently guiding an instillation tubing (PE-50; Clay Adams, Becton Dickinson and Company) to the right lung, as has been done previously (11). After instillation, the tubing was withdrawn. Arterial blood samples were obtained hourly after the instillation for measurements of 131I-albumin and 125I-albumin activity and arterial blood gas determinations. Sixty minutes after the beginning of instillation, the abdomen was opened, and the animals were exsanguinated by transecting the abdominal aorta. The lungs were removed through a median sternotomy. Alveolar liquid was sampled by gently passing the sampling catheter (PE-50) into a wedged position in the Evan's blue labeled (instilled) area of the instilled lung for measurement of total protein and radioactivity. In a prior study (4), we reported that the concentration of the protein tracers in the liquid sampled by a small catheter wedged into the distal airways was the same as in an alveolar micropuncture sample. Right and left lungs were then homogenized separately for water-to-dry weight ratio measurement and radioactivity counts.

Two hour experiments. In order to assess the net effect of dobutamine and dopamine on the removal of excess fluid from the whole lung over a longer time period, a larger volume (6 ml/kg) was instilled into both lungs so that the net removal of the excess fluid could be measured over 2 h. Arterial blood samples were obtained for measurements of arterial blood gas determinations hourly after the instillation. At the end of the study period, the rats were processed as described above. Since intra-alveolar dobutamine and dopamine had no hemodynamic effects (see RESULTS), these vasopressor agents were given by the intra-alveolar route in these experiments. In several of our prior studies, the rate of alveolar fluid clearance was independent of the instilled volume (5, 11, 14).

Left arterial pressure experiments. Because alterations in left atrial pressure might affect alveolar liquid clearance, measurements of left atrial pressure in control, intravenous and intra-alveolar dobutamine, and intravenous and intra-alveolar dopamine were obtained with a catheter inserted directly into the left atrium (see group 9 in SPECIFIC PROTOCOLS). At the end of the study, the rats were processed as above.

Specific Protocols

Group 1: control (n = 6), control + amiloride (n = 4). After the baseline period, 1 ml of a 5% albumin solution in Ringer's lactate was instilled over 20-25 min to determine basal alveolar liquid clearance in normal rats. In some rats, amiloride (10-3 M) was added to the instillate. One hour after the beginning of instillation, the rats were processed as described in the general protocol.

Group 2: dobutamine (intra-alveolar, 10-4 M, n = 6). To determine the effect of dobutamine on alveolar liquid clearance, 10-4 M dobutamine was added to the instillate. At this dosage, dobutamine has both beta-1 and beta-2 effects (12). One hour after the beginning of the instillation, the rats were processed as described in the general protocol.

Group 3: dopamine (intra-alveolar, 10-5 M, n = 2, or 10-4 M, n = 4). To determine the effect of dopamine on alveolar liquid clearance, two different doses were tested. In contrast to dobutamine, dopamine is a potent beta-1 agonist, but has beta-2 effects only at very high doses (9, 10). One hour after the beginning of instillation, the rats were processed as described in the general protocol.

Group 4: dobutamine (intravenous, 5 µg/kg/min, n = 5). To determine the effect on alveolar liquid clearance of dobutamine at a clinically relevant dosage, dobutamine was infused through a venous catheter starting 10 min before instillation. One hour after the beginning of instillation, the rats were processed as described in the general protocol.

Group 5: dopamine (intravenous, 5 µg/kg/min, n = 3 or 10 µg/kg/ min, n = 2). To determine the effect on alveolar liquid clearance of dopamine at clinically relevant doses, 5 µg /kg /min or 10 µg /kg /min of dopamine was given intravenously. At these doses, dopamine does not have beta-2 activity (9, 10). One hour after the beginning of instillation, the rats were processed as described in the general protocol.

Group 6: dobutamine (10-4 M) plus amiloride (10-3 M) (intra-alveolar, n = 4). To determine whether the increase in alveolar liquid clearance observed in the dobutamine studies was mediated by an increase in sodium uptake across the alveolar epithelial barrier, both amiloride and dobutamine were added to the instillate. One hour after the beginning of instillation, the rats were processed as described in the general protocol.

Group 7: dobutamine (10-4 M) plus ICI 118,551 (10-4 M), intra- alveolar (n = 4), and ICI 118,551 (10-4 M) alone (control), intra-alveolar (n = 4). To determine whether the dobutamine-induced increase in alveolar liquid clearance was mediated by stimulation of the beta-2 receptor, ICI 118,551 and dobutamine were added to the instillate. ICI 118,551 is a specific and potent beta-2 antagonist (13). One hour after the beginning of instillation, the rats were processed as described in the general protocol.

Group 8: 2 hr experiments, excess lung water (n = 12). To study the effects of dobutamine and dopamine on removal of fluid from both the air spaces and interstitium of the lung, 6 ml/kg of Ringer's lactate with 5% albumin and 3 µCi 125I-albumin with either dobutamine (10-4 M, n = 4), dopamine (10-4 M, n = 4), or with no drug (n = 4) were instilled into the distal trachea to distribute the fluid to both lungs. Two hours after the beginning of instillation, the rats were processed as described above with the objective of comparing the extravascular lung waters of the three groups: dopamine, dobutamine, and controls.

Group 9: left atrial pressure measurements. In order to determine the effect of dobutamine and dopamine on left atrial pressure, measurements of the left atrial pressures of rats in control (n = 6), intravenous dobutamine (5 µg/kg/min, n = 5), intra-alveolar dobutamine (10-4 M, n = 3), intravenous dopamine (5 µg/kg/min, n = 3; 10 µg/kg/ min, n = 2), and intra-alveolar dopamine (10-4 M, n = 3) were obtained with a catheter inserted directly into the left atrium. After 30 min of stable baseline, a measurement was taken every 10 min for 30 min.

Measurements

Hemodynamics, airway pressure, arterial blood gases, and protein concentration. Systemic blood and airway pressures were continuously monitored using calibrated pressure transducers (Pd23 ID; Gould, Oxnard, CA) and recorded continuously on a Grass polygraph (Grass Model 7 Polygraph; Grass Instruments, Quincy, MA), and arterial blood gases were measured every 15 min before instillation and one hour after instillation of the albumin solution. Samples of blood, instillate, and final alveolar fluid from the distal air spaces were collected to measure total protein concentration and 125I-albumin.

Lung endothelial and epithelial barrier protein permeability. Two different methods were used to measure the protein permeability of the alveolar epithelium to albumin (3). The first method required measurement of residual 125I-albumin (the air space protein tracer) in the lung as well as accumulation of 125I-albumin in the plasma. The second method required measurement of a plasma protein tracer, 131I- albumin, in the extravascular spaces of the lung.

For measuring the clearance of the alveolar tracer protein, 125I- albumin, from the lung, the total radioactivity of the instilled 125I-albumin (cpm/g) in the samples of the 5% albumin instillate was multiplied by the volume that was instilled. To calculate the quantity of the 125I-albumin in the lungs at the end of the experiment, the average of the duplicate radioactivity counts from the lung homogenate was multiplied with the volume of lung homogenate. To measure the accumulation of 125I-albumin from the alveolar spaces into the blood, the radioactivity counts in the plasma samples were multiplied by the estimated plasma volume (ml) at the time of sampling (Equation 1):

Please refer to the pdf to view this equation.

To estimate the clearance of the vascular tracer protein, 131I-albumin, into the extravascular compartments of the lungs (interstitium and air spaces), the total extravascular 131I-albumin accumulation in the alveolar liquid recovered from air spaces and in the lung homogenate was measured. Then, the amount of extravascular 131I-albumin was calculated by the following (Equation 2):

Please refer to the pdf to view this equation.

To calculate the 131I-albumin(vascular space, lung), the 131I-albumin counts in the last plasma sample were multiplied by the blood volume in the lungs, corrected for the hematocrit. If the amount of 131I-albumin in 1 ml of blood is known, the extravascular 131I-albumin represents the volume of plasma that had leaked out from the blood vessels during the experiment.

Trichloroacetic acid (TCA) precipitation was carried out on the instillates and on selected samples from each experiment; it was established that both of the tracers, 125I and 131I, were always more than 98% bound to the protein.

Estimate of alveolar liquid clearance. As in previous studies, alveolar liquid clearance was estimated by measuring the increase in the final alveolar protein concentration compared with the initial alveolar (instilled) protein concentration. Because the volume of instillate is known, the following proportion (Equation 3) can be used:
alveolar liquid clearance=[V<SUB>i</SUB>−(V<SUB>i</SUB>×P<SUB>i</SUB>/P<SUB>f</SUB>)/V<SUB>i</SUB>]×100 (3)

in which Vi is the instilled volume, Pi is the initial protein concentration, and Pf is the final protein concentration. This equation was used with protein values derived from the Biuret method and radioactive counts of 125I-albumin.

Lung liquid clearance (excess lung water measurement). To determine the extravascular water in the lungs of the rats in the 2 h studies (Group 8), standard methods were used as in prior studies (5). Before exsanguination, a blood sample was obtained to measure the hemoglobin concentration and the water to dry weight ratio of blood for the lung water calculation. The lungs were homogenized and the extravascular lung water was determined by calculating the water to dry weight ratio.

Determination of plasma concentration of epinephrine. Plasma epinephrine values were measured by high pressure liquid chromatography by a laboratory technician blinded to the conditions of the experiments. Plasma was taken from the animal at the end of the experiment. One ml of blood was collected in a heparinized tube, as we have done before (2). Blood samples were immediately centrifuged at 5,000 g for 5 min at +4° C; 0.5 ml of plasma was transferred to an Eppendorf tube and quickly frozen to -70° C in acetone and dry ice. Samples were stored at -70° C until analyzed. Plasma samples were spiked with an internal standard and absorbed on activated alumina at alkaline pH. Epinephrine was eluted by 0.1 M perchloric acid, analyzed by reverse-phase HPLC using a C8 column, and measured by the amperometric method using an electrochemical detector. Correlation coefficient and detection limit of this method were 0.96 and 10 pg/ml, respectively.

Statistics. Data is presented as mean ± standard deviation. Experimental groups were compared to controls using one way analysis of variance (ANOVA) with Student-Newman Keuls test as post hoc. p Value < 0.05 was considered significantly different.

    RESULTS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Alveolar Liquid Clearance

Effects of dobutamine and dopamine. Basal alveolar liquid clearance in anesthetized, ventilated rats was 22 ± 6% of the instilled volume over one hour (Table 1, Figure 1). Intra-alveolar dobutamine (10-4 M) significantly increased alveolar liquid clearance by 59%, whereas intra-alveolar dopamine (10-4, 10-5 M) did not affect clearance (Table 1, Figure 1). Similarly, intravenous dobutamine (5 µg/kg/min) significantly increased alveolar liquid clearance by 45%, but intravenous dopamine (5-10 µg/kg/min) had no effect on alveolar liquid clearance (Table 1, Figure 2). Overall, there was a good correlation between alveolar liquid clearance calculated from the concentration of 125I-albumin and the concentration of unlabeled protein (r 2 = 0.85).

                              
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TABLE 1

EFFECT OF DOBUTAMINE AND DOPAMINE ON ALVEOLAR LIQUID CLEARANCE OVER 1 h


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  		Figure 1.   Effects of intra-alveolar dobutamine and dopamine on alveolar liquid clearance calculated from concentration of 125I- albumin. Alveolar liquid clearance over one hour increased to 35 ± 6% with 10-4 M dobutamine compared to 22 ± 6% for controls and 20 ± 6% for dopamine 10-4 and 10-5 M. Data shown as mean ± SD. *p < 0.05 versus control and dopamine.


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  		Figure 2.   Effects of intravenous dobutamine and dopamine on alveolar liquid clearance calculated from concentration of 125I-albumin. Alveolar liquid clearance over one hour increased to 32 ± 4% with 5 µg/kg/min dobutamine compared to 22 ± 6% for controls and 22 ± 2% for dopamine 5-10 µg/kg/min. Data shown as mean ± SD. *p < 0.05 versus control and dopamine.

Effect of amiloride. Amiloride (10-3 M) prevented the increase in the final to initial protein ratio in the dobutamine instilled rats compared with dobutamine alone (1.29 ± 0.02 versus 1.57 ± 0.23, p < 0.05). Thus, the calculated alveolar liquid clearance in rats instilled with dobutamine plus amiloride was similar to controls. The effect of amiloride under control conditions is also shown (Figure 3).


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  		Figure 3.   Effects of intra-alveolar amiloride on alveolar liquid clearance calculated from concentration of 125I-albumin. Amiloride 10-3 M inhibited clearance in control and dobutamine treated rats though there is clearly an amiloride-insensitive component under both control and stimulated (dobutamine) conditions. Data shown as mean ± SD. *p < 0.05 versus control and dagger p < 0.005 versus dobutamine plus amiloride.

Effect of beta-2 adrenergic receptor inhibitor. The specific beta-2 inhibitor, ICI 118,551, completely blocked the dobutamine induced increase in alveolar liquid clearance (Table 2, Figure 4).

                              
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TABLE 2

EFFECTS OF ICI 118,551 ON ALVEOLAR LIQUID CLEARANCE OVER 1 h


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  		Figure 4.   Effects of intra-alveolar ICI 118,551 on alveolar liquid clearance calculated from concentration of 125I-albumin. ICI 118,551 10-4 M blocked the dobutamine effect and returned clearance to control levels. Rats given ICI 118,551 10-4 M alone also had alveolar liquid clearance rates similar to controls (20 ± 3%). Data shown as mean ± SD. *p < 0.05 versus control, dobutamine + ICI, and control + ICI.

Effect of dobutamine on removal of excess fluid from the lung over two hours. Two hours-after instillation of 6 ml/kg, rats treated with intra-alveolar dobutamine had significantly less extravascular lung water than controls, whereas extravascular lung water in rats treated with dopamine were similar to controls (Table 3).

                              
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TABLE 3

EFFECTS OF INTRA-ALVEOLAR DOBUTAMINE AND DOPAMINE ON LUNG LIQUID CLEARANCE OVER 2 h

Endogenous catecholamines. Epinephrine levels were studied in rats from each experimental group, and all groups had levels of endogenous catecholamines within the normal range.

Hemodynamic measurements. Intravenous dobutamine and intravenous dopamine increased the heart rate significantly (Table 4). However, there was no significant effect on systolic or diastolic blood pressures (Table 4). Left atrial pressure was not altered by intra-alveolar dobutamine, but intravenous dobutamine and both intra-alveolar and intravenous dopamine tended to decrease left atrial pressures by on average 1.5 cm H2O (Table 4). There were no effects on airway pressures from either dopamine or dobutamine. Also, neither of the inhibitors, amiloride or ICI 118,551, affected the hemodynamic parameters measured (data not shown).

                              
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TABLE 4

SYSTEMIC HEMODYNAMICS IN RATS TREATED WITH INTRA-ALVEOLAR OR INTRAVENOUS DOBUTAMINE OR DOPAMINE

Tracer protein flux. There were no effects of dopamine or dobutamine on the bidirectional movement of 131I-albumin (vascular tracer) into the extravascular spaces of the lung or on the accumulation of 125I-albumin (alveolar tracer) in the plasma compared to controls (data not shown).

    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

The primary objective of this study was to determine the effects of dobutamine and dopamine, two commonly used vasopressors, on alveolar liquid clearance and to distinguish between beta-1 and beta-2 stimulation of alveolar fluid clearance. Both intra-alveolar and intravenous dobutamine significantly increased alveolar liquid clearance, whereas rats given intra-alveolar or intravenous dopamine had clearance rates similar to controls (Figure 1). The results indicate that dobutamine increases alveolar liquid clearance by stimulating vectorial sodium transport by the beta-2 receptor.

In order to examine the effect of the dobutamine and dopamine on alveolar liquid clearance, the drugs were administered to anesthetized, ventilated rats by two different methods. First, the drugs were instilled directly into the distal air spaces. This method delivers a high concentration of drug locally to the alveolar epithelium and allows analysis of the effect in the absence of systemic hemodynamic effects. Second, the drugs were delivered by intravenous infusion to study their effects at clinically relevant doses.

Alveolar liquid clearance was measured by the ratio of final to initial protein concentration. This method reflects the ability of the alveolar epithelium to remove fluid from the air spaces since the intact epithelium is virtually impermeable to proteins. Thus, clearance can be measured as a percentage of the instilled volume that is removed from the air spaces by the increase in concentration of protein in the air spaces over time (3, 6, 14). Lung liquid clearance was measured by the gravimetric method to determine extravascular lung water in the two hour experiments.

In these experiments, intra-alveolar dobutamine significantly increased liquid clearance by 59% relative to controls, while rats treated with intra-alveolar dopamine had clearance rates similar to controls (Table 1, Figure 1). In addition, intravenous dobutamine significantly increased alveolar liquid clearance by 45% over controls whereas intravenous dopamine-treated rats were again similar to controls (Table 1, Figure 2). The effect of dobutamine and dopamine on lung liquid clearance was measured over 2 h in rats instilled with 6 ml/kg of a 5% albumin solution. In the rats given intra-alveolar dobutamine, extravascular lung water was significantly less than in controls, indicating that clearance from both the air spaces and interstitium was increased in the dobutamine treated group (Table 3). The rats that were given dopamine, however, had extravascular lung water values similar to controls.

Once it was determined that dobutamine, not dopamine, increased alveolar liquid clearance, the second objective was to study the mechanism to account for the increase in clearance. Beta-adrenergic agonists have previously been shown to increase sodium transport and alveolar liquid clearance in cultured alveolar type II epithelial cells (15), the resected human lung (6), and several animal species (1). In this study, treatment with amiloride (10-3 M), a sodium channel blocker, inhibited the dobutamine-induced increase in alveolar liquid clearance (Figure 3), confirming that the effect of dobutamine was dependent on the uptake of sodium by the alveolar epithelium.

Since dobutamine and dopamine are both beta-agonists, it is important to account for their differential effects on alveolar liquid clearance. Dobutamine is an agonist for both beta-1 and beta-2 receptors, but dopamine, well known for its beta-1 effects, has very little affinity for the beta-2 receptor. In fact, dopamine has less than 1/60 of norepinephrine's affinity for the beta-2 receptor (10, 16). We postulated that dobutamine's effect on clearance may be due to stimulation of the beta-2 receptor. ICI 118,551 is a specific antagonist of the beta-2 receptor, and rats instilled with both ICI 118,551 and dobutamine had clearance rates similar to controls (Figure 4). Blockade of stimulated clearance by specific antagonism of the beta-2 receptor indicates that stimulation of this receptor is responsible for the upregulation of sodium transport. Also, there is autoradiographic evidence that beta-2 receptors outnumber beta-1 receptors by a two to one ratio in the human alveolar epithelium (7, 17).

Could the dobutamine effect have been mediated by some other mechanism, such as the endogenous release of epinephrine? This seemed unlikely, but to be certain, plasma epinephrine levels in each experimental group were measured. Plasma epinephrine levels in each group were similar to controls, confirming that endogenous release of epinephrine was not responsible for the dobutamine-induced increase in clearance.

Could a change in hemodynamic pressures have influenced the results? For example, dopamine can cause a modest increase in left atrial pressure and dobutamine may cause a modest decrease in left atrial pressure (18). To examine these effects, left atrial pressures were measured in rats given either intra-alveolar or intravenous dobutamine or dopamine. These measurements confirmed that left atrial pressures were not elevated in any groups. Intravenous dobutamine lowered left atrial pressure compared to controls, but there were no other significant differences among the experimental groups (Table 4). These data support the conclusion that dobutamine's effect on alveolar liquid clearance relative to dopamine is due to stimulation of the beta-2 adrenergic receptor, and not due to the hemodynamic effect.

The effect of amiloride, an inhibitor of apical sodium channel uptake, was studied under control conditions as well as in the presence of dobutamine (Figure 3). The dose of amiloride 10-3 M that was used in these studies may have effects on other transport pathways besides apical membrane uptake of sodium. However, amiloride is 50% protein bound and a significant fraction of amiloride escapes from the airspaces rapidly in vivo (19). Therefore, the actual concentrations of amiloride at the apical membrane of alveolar epithelial cells in vivo was probably 10-4 M, or less.

A second issue concerns the fraction of basal and stimulated clearance that is amiloride-insensitive. Only 50% of both basal and stimulated clearance was inhibited by amiloride. Some alveolar fluid may have escaped by a paracellular pathway, but this is less likely since alveolar protein concentration increased over 8 g/100 ml in the dobutamine studies. If a passive, paracellular pathway was involved, it would be unlikely that these high alveolar protein concentrations could be achieved. Another possibility is that the non-amiloride-sensitive fraction represents poorly defined cation channels that are not inhibited by amiloride.

There is another recent preliminary report that dopamine modestly increased alveolar fluid clearance in an isolated perfused rat lung preparation (20). The effect of dopamine in that preparation might be mediated by beta-2 adrenergic stimulation because the effective dose could be much higher in the perfused lung than in our in vivo preparation. Alternatively, there might be another pathway that is stimulated in that preparation.

There are important clinical implications of this study. Dobutamine and dopamine are the two most commonly used vasoactive agents in the intensive care unit. Dobutamine is a primary inotropic agent frequently used for patients with moderate to severe congestive heart failure and pulmonary edema (21). Dopamine has a wider clinical application including treatment for systemic hypotension in patients with sepsis, the acute respiratory distress syndrome (ARDS), and to increase renal vascular perfusion in low output states (22). In ARDS, increased endothelial and epithelial permeability from a variety of insults to the lung leads to the accumulation of protein rich edema fluid in the air spaces. Interestingly, in a canine model of oleic acid induced pulmonary edema, a continuous infusion of dobutamine reduced extravascular lung water compared with controls, although some of the effect was accounted for by a decrease in left atrial pressure (23).

In patients with pulmonary edema from congestive heart failure, dobutamine decreases systemic vascular resistance and left ventricular after-load in addition to decreasing left atrial pressure (18). In this study, dobutamine increased alveolar liquid clearance in anesthetized, ventilated rats by beta-2 receptor stimulation. Therefore, an additional mechanism by which dobutamine may accelerate the resolution of pulmonary edema is by direct stimulation of the beta-2 receptor to increase alveolar fluid clearance.

Could dobutamine be of potential value in the treatment of acute lung injury? Since beta-2 receptor stimulation can increase alveolar liquid clearance, treatment with dobutamine might hasten the resolution of alveolar edema. Second, beta-agonist stimulation may increase surfactant production by alveolar type II cells, an effect that may improve the mechanical properties of the injured lung. Third, there are some studies which have demonstrated that increases in intracellular cAMP by beta-adrenergic agonist can attenuate the increase in lung endothelial permeability (24, 25) perhaps by inhibiting endothelial gap formation (26). These issues should be experimentally addressed in studies of acute lung injury using dobutamine in clinically relevant doses.

Several investigators have studied the upregulation of alveolar epithelial sodium and fluid transport by catecholamine-dependent and catecholamine-independent mechanisms (27- 31). In the clinical setting of acute lung injury, it is possible for excess alveolar fluid to be removed early in the course of lung injury (32). There are several endogenous and potentially exogenous (i.e., pharmacologic) mechanisms that may increase alveolar fluid clearance. More work on the interaction of these mechanisms in both experimental models of acute lung injury and in clinical studies is needed.

In summary, dobutamine upregulates alveolar liquid clearance in rats through stimulation of the beta-2 receptor. Thus, the beta-2 adrenergic receptor is responsible for stimulating vectorial sodium and fluid transport. Since dobutamine is a commonly used vasoactive agent in the intensive care unit, these results may have clinical implications for the pharmacologic management of pulmonary edema.

    Footnotes

Correspondence and requests for reprints should be addressed to Michael A. Matthay, M.D., Cardiovascular Research Institute, Box 0130, University of California, San Francisco, CA 94143-0130. E-mail: mmatt{at}itsa.ucsf.edu

(Received in original form September 30, 1996 and in revised form March 6, 1997).

Acknowledgments: The authors wish to thank Oscar Osorio for his technical assistance.

Supported by NIH HL 51854 and Dr. Folkesson was supported by a California Lung Association Fellowship Award and Dr. Chesnutt by an Allen Hanbury's Research Fellowship.

    References
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

1. Crandall, E. D., T. H. Hemming, R. L. Palombo, and B. E. Goodman. 1986. Effect of terbutaline on sodium transport in isolated perfused rat lung. J. Appl. Physiol 60: 289-294 [Abstract/Free Full Text].

2. Pittet, J. F., J. P. Wiener-Kronish, M. C. McElroy, H. G. Folkesson, and M. A. Matthay. 1994. Stimulation of lung epithelial liquid clearance by endogenous release of catecholamines in septic shock in anesthetized rats. J. Clin. Invest 94: 663-671 .

3. Berthiaume, Y., N. C. Staub, and M. A. Matthay. 1987. Beta-adrenergic agonists increase lung liquid clearance in anesthetized sheep. J. Clin. Invest 79: 335-343 .

4. Berthiaume, Y., V. C. Broaddus, M. A. Gropper, T. Tanita, and M. A. Matthay. 1988. Alveolar liquid and protein clearance from normal dog lungs. J. Appl. Physiol 65: 585-593 [Abstract/Free Full Text].

5. Jayr, C., C. Garat, M. Meignan, J. F. Pittet, M. Zelter, and M. A. Matthay. 1994. Alveolar liquid and protein clearance in anesthetized ventilated rats. J. Appl. Physiol 76: 2636-2642 [Abstract/Free Full Text].

6. Sakuma, T., G. Okaniwa, T. Nakada, T. Nishimura, S. Fujimura, and M. A. Matthay. 1994. Alveolar fluid clearance in the resected human lung. Am. J. Respir. Crit. Care Med 150: 305-310 [Abstract].

7. Carstairs, J. R., A. J. Nimmo, and P. J. Barnes. 1985. Autoradiographic visualization of beta-adrenoceptor subtype in human lung. Am. Rev. Respir. Dis 132: 541-547 [Medline].

8. Barnes, P.. 1995. Beta-adrenergic receptors and their regulation. Am. J. Respir. Crit. Care Med 152: 838-860 [Medline].

9. Goldberg, L. I.. 1972. Cardiovascular and renal actions of dopamine. Pharm. Rev 24: 1-29 [Free Full Text].

10. Waldeck, B.. 1977. Analysis of the beta -receptor mediated effect on slow contracting skeletal muscle in vitro. J. Pharm. Pharmac 29: 550-554 [Medline].

11. Folkesson, H. G., J.-F. Pittet, G. Nitenberg, and M. A. Matthay. 1996. Transforming growth factor-alpha increases alveolar liquid clearance in anesthetized ventilated rats. Am. J. Physiol 271: L236-L244 [Abstract/Free Full Text].

12. Ruffolo, R. R. Jr., T. A. Spradlin, G. D. Pollock, J. E. Waddell, and P. J. Murphy. 1981. Alpha and beta adrenergic effects of the stereoisomers of dobutamine. J. Pharmacol. Exp. Ther 219: 447-452 [Abstract/Free Full Text].

13. Bilski, A. J., S. E. Halliday, J. D. Fitzgerald, and J. L. Wale. 1983. The pharmacology of a beta-2 selective adrenoceptor antagonist (ICI 188,551). J. Cardiovasc. Cardiol 5: 430 .

14. Smedira, N., L. Gates, R. Hastings, C. Jayr, T. Sakuma, J.-F. Pittet, and M. A. Matthay. 1991. Alveolar and lung liquid clearance in anesthetized rabbits. J. Appl. Physiol 70: 1827-1835 [Abstract/Free Full Text].

15. Goodman, B. E., R. S. Fleischer, and E. D. Crandall. 1983. Evidence for active Na+ transport by cultured monolayers of pulmonary alveolar epithelial cells. Am. J. Physiol 245: C78-C83 [Abstract/Free Full Text].

16. McNay, J. L., and L. I. Goldberg. 1966. Comparison of the effects of dopamine, isoproterenal, norepinephrine, and bradykinin on canine renal and femoral blood flow. J. Pharmacol. Exp. Ther 151: 23-31 [Abstract/Free Full Text].

17. Mak, J. C. W., M. Nishikawa, and P. J. Barnes. 1994. Localization of beta -adrenoceptor subtype mRNAs in human lung. Am. J. Respir. Crit. Care Med 149(Suppl.): 1027 .

18. Leier, C. V., P. T. Heban, P. Huss, C. Bush, and R. Lewis. 1978. Comparative systemic and regional hemodynamic effects of dopamine and dobutamine in patients with cardiomyopathic heart failure. Circulation 58: 466-475 [Abstract/Free Full Text].

19. O'Brodovich, H., V. Hannam, and B. Rafii. 1991. Sodium channel but neither Na ± H+ nor NA-glucose inhibitors slow neonatal lung water clearance. Am. J. Respir. Cell Mol. Biol 5: 377-384 .

20. Barnard, M. L., W. G. Olivera, D. M. Rutschman, A. I. Katz, and J. I. Sznajder. 1996. Dopamine stimulates sodium transport and liquid clearance in rat lung epithelium (abstract). FASEB J 10: 349A .

21. Chatterjee, K. 1988. Digitalis, catecholamines, and other positive inotropic agents. In W. W. Parmley and K. Chatterjee, editors. Cardiology, Vol. 1. J. B. Lippincott Co., Philadelphia, PA. 1-46.

22. Matthay, M. A., and V. C. Broaddus. 1994. Fluid and hemodynamic management in acute lung injury. Sem. Resp. Med 15: 271-288 .

23. Molloy, W. D., K. Y. Lee, L. Girling, and R. Prewitt. 1984. Treatment of canine permeability pulmonary edema: short-term effects of dobutamine, furosemide, and hydrazine. Circulation 72: 1365-1371 [Abstract/Free Full Text].

24. Adkins, W. K., J. W. Barnard, A. R. Seibert, J. Haynes, and A. E. Taylor. 1992. Compounds that increase cAMP prevent ischemia-reperfusion pulmonary capillary injury. J. Appl. Physiol 72: 492-497 [Abstract/Free Full Text].

25. Seibert, A. F., J. Thompson, A. E. Taylor, W. H. Wolborn, J. Barnard, and J. Haynes. 1992. Reversal of increased microvascular permeability associated with ischemia-reperfusion: role of cAMP. J. Appl. Physiol 22: 389-395 .

26. Baluk, P., and D. M. McDonald. 1994. The beta 2-adrenergic receptor agonist, formoterol reduces microvascular leakage by inhibiting endothelial gap formation. Am. J. Physiol 266: L461-L468 [Abstract/Free Full Text].

27. Matthay, M. A., H. G. Folkesson, and A. S. Verkman. 1996. Salt and water transport across alveolar and distal airway epithelia in the adult lung. Am. J. Physiol. L487-L503.

28. Matalon, S., D. J. Benos, and R. M. Jackson. 1996. Biophysical and molecular properties of amiloride-inhibitable sodium channels in alveolar epithelial cells. Am. J. Physiol 271: L1-L22 [Abstract/Free Full Text].

29. Sznajder, J. I., W. G. Olivera, K. M. Ridge, and D. H. Rutschman. 1995. Mechanisms of lung liquid clearance during hyperoxia in isolated rat lungs. Am. J. Respir. Crit. Care Med 151: 1519-1525 [Abstract].

30. Borok, Z., S. J. Danto, R. L. Lubman, K. J. Kim, and E. D. Crandall. 1996. Effects of EGF on alveolar epithelial junctional permeability and active sodium transport. Am. J. Physiol 270: L559-L565 [Abstract/Free Full Text].

31. Nici, L., R. Dowin, M. Gilmore-Herbert, J. D. Jamieson, and D. H. Ingbar. 1991. Upregulation of rat lung Na-K-ATPase during hyperoxic lung injury. Am. J. Physiol 261: L307-L314 [Abstract/Free Full Text].

32. Matthay, M. A., and J. P. Weiner-Kronish. 1990. Intact alveolar epithelial barrier function is critical for the resolution of alveolar edema in humans. Am. Rev. Respir. Dis 142: 1250-1257 [Medline].




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