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(Chest. 2005;128:3743-3749.)
© 2005 American College of Chest Physicians

Comparative Effects of Salmeterol, Albuterol, and Ipratropium on Normal and Impaired Mucociliary Function in Sheep*

Juan R. Sabater, MD; Troy A. Lee, BS and William M. Abraham, PhD

* From the Division of Pulmonary and Critical Care Medicine, Miller School of Medicine, University of Miami at Mount Sinai Medical Center, Miami Beach, FL.

Correspondence to: William M. Abraham, PhD, Department of Research, Mount Sinai Medical Center, 4300 Alton Rd, Miami Beach, FL 33140; e-mail: abraham{at}msmc.com


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objective: We measured tracheal mucus velocity (TMV), a marker of mucociliary clearance (MCC), in sheep before and for 12 h after treatment with salmeterol, albuterol, ipratropium, or vehicle to determine the effects on normal MCC. We also determined if these agents could reverse the depression in TMV caused by inhaled human neutrophil elastase (HNE), a model of abnormal MCC.

Methods: Study 1: TMV was measured initially and then for 6 h after metered-dose inhaler treatment with salmeterol (42 µg), albuterol (180 µg), ipratropium bromide (36 µg), or vehicle. After 6 h, the sheep in the albuterol and ipratropium treatment arms were administered a second dose of drug, whereas the salmeterol and vehicle treatment arms received vehicle. TMV was measured for another 6 h. Study 2: Six sheep inhaled HNE aerosol, which significantly reduced TMV by 2 h. At this point, the sheep were treated with either salmeterol, albuterol, ipratropium, or vehicle, and the effects on TMV were measured for another 6 h. This experiment was repeated in four sheep using only salmeterol and albuterol, but the posttreatment measurements were extended to 12 h.

Results: Study 1: Only salmeterol and albuterol increased TMV (p < 0.05) during the initial 6-h period. From 6 to 12 h only, the salmeterol-treated sheep had TMV that remained at or above the initial TMV for the entire time, although both albuterol and ipratropium showed enhancement of TMV compared to vehicle. Study 2: Salmeterol and albuterol reversed the HNE-induced depression in TMV to a similar degree over the 6-h time course. However, the protection afforded by salmeterol was more prolonged than that seen with albuterol if the posttreatment interval was extended to 12 h. Ipratropium and vehicle had no effect.

Conclusion: We conclude that salmeterol and albuterol can stimulate normal MCC and reverse HNE-induced mucociliary dysfunction and that salmeterol has a longer duration of action in these models of normal and abnormal MCC.

Key Words: anticholinergics • ß-adrenergics • COPD • cystic fibrosis • elastase • mucociliary clearance • tracheal mucus velocity


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Impaired airway mucociliary clearance (MCC) is a central component of the pathophysiology of asthma, COPD, and cystic fibrosis (CF).1 ß-Adrenergic agents have been used in the treatment of all three diseases, not only because they relax airway smooth muscle, but because of a prominent non-smooth muscle effect: enhancement of MCC.2 ß-Agonists have multiple effects on airway epithelial cells, including stimulating ciliary beat frequency13 and stimulation of chloride secretion toward the airway lumen,4 which theoretically could improve the hydration state of the mucus by increasing the water secretion onto the airway surface. Both of these mechanisms could contribute to the enhanced MCC observed in vivo with ß-adrenergics.12

Most previous studies2 examining the effects of ß-adrenergic agents on MCC were conducted with a variety of short-acting agents. While these agents have been effective in stimulating mucus clearance, they suffer from a short duration of action and so require multiple administrations over the course of 24 h. This shortcoming resulted in the development of long-acting ß-adrenergic agents, eg, salmeterol and formoterol.5 These agents have clearly shown their superior duration of action in terms of bronchodilation5; however, there have been relatively few studies26 comparing their effects on MCC to determine if the long-acting agonists provide any advantage over their short-acting counterparts.

We have studied a number of compounds reported to stimulate whole-lung MCC clearance or tracheal mucus velocity (TMV), a marker of MCC, in sheep.789 Changes in MCC seen in this model under normal and impaired conditions in the presence and absence of therapeutic intervention mimic responses observed in healthy individuals and subjects with airway disease.1011 Thus, the model can be used for comparative purposes to address questions of efficacy among different drugs and so could be used to assess potential advantages of long-acting vs short-acting ß-adrenergic agents.

While the ability to improve MCC in normal airways is informative in terms of therapeutic potential, it may be more important to determine if an agent can block or reverse mucociliary dysfunction. A common inflammatory mediator that contributes to impaired mucus clearance in asthma, COPD, and CF is neutrophil elastase.1213141516 Elastase is a known mucus secretagogue,1718 has cilio-inhibitory properties,1920 and can stimulate epithelial sodium channels, which reduces the periciliary fluid layer contributing to mucus stasis.21 These collective actions of elastase on the various components of mucociliary function are consistent with our in vivo observations showing that inhaled elastase depresses MCC, as measured by TMV, for up to 8 h in sheep.10 The elastase-induced depression in TMV can be prevented and reversed with natural and synthetic elastase inhibitors including {alpha}1-protease inhibitor,10 secretory leukocyte protease inhibitor,22 and a synthetic human neutrophil elastase (HNE) inhibitor.10 There is little information, however, on the ability of ß-adrenergic agents or other agents, eg, anticholinergics, used in the treatment of asthma, COPD, and CF to improve the elastase-induced impairment in TMV. In this study, we addressed two questions: we compared the effects of inhaled salmeterol, a long-acting ß-adrenergic agonist, with that of the short-acting ß-adrenergic agonist albuterol, and ipratropium bromide (ipratropium), an anticholinergic agent, on normal MCC in sheep as measured by TMV; and we tested the ability of these agents to reverse the impaired transport caused by inhaled human HNE.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Animal Preparation
The Mount Sinai Medical Center Animal Research Committee, which is responsible for ensuring the humane care and use of experimental animals, approved all procedures used in this study. The sheep were conscious throughout these studies. Instrumentation was performed under local anesthesia.

To study the effects of the different agents on TMV, the sheep, after topical anesthesia of the nasal passages with 2% lidocaine solution, were nasally intubated with a shortened endotracheal tube 7.5 cm in diameter (Mallinckrodt Medical; St. Louis, MO). The cuff of the tube was placed just below the vocal cords (verified by fluoroscopy) to allow for maximal exposure of the tracheal surface area. To minimize possible impairment of TMV caused by endotracheal tube cuff inflation, we deflated the cuff throughout the study except for the period of drug delivery.7 To alleviate the effects of prolonged intubation, we warmed and humidified the inspired air (Bennett Humidifier; Puritan-Bennett; Lenexa, KS).

TMV was measured in vivo by a roentgenographic technique. Five to 10 radiopaque Teflon/bismuth trioxide disks, 1 mm in diameter, 0.8-mm thick, and 1.8 mg in weight, were insufflated onto the trachea. A modified suction catheter connected to a source of continuous compressed air at a flow of 3 to 4 L/min was used to introduce the particles via the endotracheal tube. The catheter remains within the endotracheal tube only, so that no contact with the tracheal surface is made. The cephalad-axial velocities of the individual disks were recorded on videotape from a portable image intensifier unit. Individual disk velocities were calculated by measuring the distance traveled by each disk during a 1-min observation period. For each run, the mean value of all individual disk velocities was calculated. A collar containing radiopaque reference markers of known length was worn by the sheep and was used as a standard to correct for magnification effects inherent in the fluoroscopy unit.7

Agents
HNE was obtained from Elastin Product Company (Owensville, MO). A stock solution was prepared according to the specifications of the manufacturer. Aliquots of 25 µL containing 2.55 U of active enzyme were prepared from stock and stored at 70°C. On the experimental day, the HNE was dissolved in 3 mL phosphate-buffered saline solution, and the sheep were administered the total amount. Ipratropium bromide was obtained from the medical center pharmacy. To control for the chlorofluorocarbon propellants in the ipratropium bromide, GlaxoSmithKline provided the salmeterol and albuterol (both in dichlorofluoromethane and trichlorofluoromethane with lecithin) and vehicle control (dichlorodifluoromethane and trichlorofluoromethane with lecithin) metered-dose inhalers (MDIs).

Aerosol Delivery Systems
Aerosols of HNE were generated using a nebulizer (Raindrop; Nellcor Puritan Bennett; Carlsbad, CA). As reported in detail,10 we used a dosimeter-piston ventilator system with this nebulizer to deliver aerosols directly into the endotracheal tube on inspiration at a tidal volume of 500 mL and a rate of 20 breaths/min. The output of the nebulizer was directed into a plastic T piece that was interconnected between the inspiratory port of a Harvard piston respirator (Harvard Apparatus; Holliston, MA) and the tracheal tube of the animal. To control aerosol delivery, a dosimeter system consisting of a solenoid valve and a source of compressed air (20 pounds per square inch) was used. The solenoid valve was activated for 1 s at the beginning of the inspiratory cycle of the respirator. This same system was used to deliver the drugs by MDI, by replacing the nebulizer with the MDI and manually activating the device during the inspiratory cycle of the respirator.

Protocols
Protocol 1: Effect of Standard Treatment With Salmeterol, Albuterol, Ipratropium, and Vehicle on Normal TMV Over 12 h:
Initial measurements of TMV were obtained, and then the sheep were treated with albuterol (two puffs by MDI, 180 µg), ipratropium (two puffs by MDI, 36 µg), salmeterol (two puffs by MDI, 42 µg), or vehicle (two puffs by MDI). Measurements of TMV were obtained 15 min, 30 min, and 45 min after treatment and then hourly after treatment for up to 6 h. After the 6-h measurement, the sheep in the albuterol, ipratropium, and placebo treatment arms received a second dose of their respective drugs: albuterol (two puffs), ipratropium (two puffs), or vehicle (two puffs), and TMV was measured 15 min, 30 min, and 45 min after this second dose and then hourly after treatment to 12 h. The sheep in the salmeterol treatment arm received vehicle (two puffs) at this 6-h time point, and TMV was measured as described above. This study was conducted in the same six sheep using a randomized, crossover design. There was a minimum of 7 days between studies in any one animal.

Protocol 2: Effects of Salmeterol, Albuterol, and Ipratropium on HNE-Induced Mucociliary Dysfunction:
Initial measurements of TMV were obtained, and then the sheep were challenged with HNE (2.55 U in 3 mL of phosphate-buffered saline solution). TMV was measured 30 min after HNE challenge and then 1 h and 2 h after challenge. The sheep were treated with salmeterol (two puffs by MDI), albuterol (two puffs by MDI), ipratropium (two puffs by MDI), or placebo (two puffs by MDI). Measurements of TMV were obtained 15 min, 30 min, and 45 min after treatment and then hourly after treatment for up to 8 h. This study was conducted in the same six sheep using a randomized, crossover design. There was a minimum of 7 days between studies in any one animal.

We repeated this study in four sheep but extended the observation time to 14 h. For this study, the same four sheep, using a randomized, crossover design, were treated with either albuterol (two puffs by MDI) or salmeterol (two puffs by MDI), or placebo (two puffs by MDI), and TMV was measured as described above. There was a minimum of 7 days between studies in any one animal.

Statistical Analysis
Data in the text, figures, and tables are presented as mean ± SE. To compare the effects of the various treatments on normal TMV, the area under the curve (AUC) for each drug was computed using the trapezoid rule. AUCs were calculated for the initial 0–6-h period, the 6- to 12-h period, and the total period. Data were log10 transformed and then analyzed by a repeated-measures analysis of variance. If a significant difference was found, the data were analyzed using a Tukey test to determine which individual treatments differed. In the case where two treatments were administered (ie, for albuterol and ipratropium), a paired t test was used to determine if the response to the two treatments differed. A two-way, repeated-measures analysis of variance was used for the studies examining the effects of the drugs on HNE-induced mucociliary dysfunction. If there was a significant interaction (drug x time), a Tukey test was used to determine significant pairwise differences. Significance was accepted at p < 0.05.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Table 1 gives the starting TMV values for all studies. There were no statistical differences in the starting values within a specific protocol. The overall time course for the effects of the different drugs on normal TMV is shown Figure 1 . In the vehicle treatment arm, TMV slowly decreased from the starting value (ie, 100%) over the course of the 12-h study to 82 ± 4%. The fall in the 12-h TMV below the starting value was also seen when the animals were treated with ipratropium and albuterol. This contrasts with the results from the salmeterol treatment arm, where TMV was maintained above or at the starting value (ie, ≥ 100%) for the entire 12-h period.


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  		Table 1. Initial Values for TMV*

 


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  		Figure 1. Effects of salmeterol (42 µg), albuterol (180 µg), ipratropium (36 µg), and vehicle on TMV in unchallenged sheep. Treatments (upward arrows) were administered after obtaining the initial TMV value and after obtaining the 6-h TMV value. After 6 h, the sheep in the albuterol and ipratropium treatment arms received a second dose of drug. Sheep in the salmeterol and placebo treatment arms received only vehicle. TMV values are expressed as a percentage of the starting TMV value. Values are mean ± SE for six sheep.

 
Analysis of the AUCs for the initial treatment period (0 to 6 h) indicated that both albuterol and salmeterol significantly (p < 0.05) increased TMV when compared to vehicle (Fig 2 ; Table 2 ). Ipratropium demonstrated a partial effect, but the response did not achieve statistical significance (p < 0.07).



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  		Figure 2. Results from Figure 1 expressed as AUC. Salmeterol and albuterol increased TMV during the initial 6-h period, compared to ipratropium and vehicle. From 6 to 12 h, only salmeterol-treated sheep had TMV at or above the initial value, but all treatments were different from vehicle. Overall (0 to 12 h), the effects of salmeterol and albuterol were different from ipratropium and vehicle (see Table 2). Values are mean ± SE for six sheep. *p < 0.05 vs vehicle.

 

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  		Table 2. Effect of Treatments on TMV in Sheep*

 
Analysis of the second treatment period (6 to 12 h) AUCs indicated that TMV was significantly faster (p < 0.05) in all the treatment groups with respect to vehicle (Fig 2; Table 2). However, as illustrated in Figure 2, only the salmeterol treatment arm had an AUC that remained positive for the entire duration of the study. Thus, despite the increase in TMV seen after the second treatment with albuterol and ipratropium, these drugs failed to maintain TMV above the initial starting value for the remaining 6-h duration. It is also of interest that following the second treatment, the AUC in TMV with albuterol was smaller (p < 0.001, paired t test) than after the first treatment. The AUC for ipratropium showed a similar trend (p < 0.08, paired t test). Considering the overall effects of treatment (AUC 0 to 12 h), both salmeterol and albuterol were significantly better than ipratropium in maintaining TMV (Table 2).

It should be noted that the analysis in Figure 2 and Table 2 was based on the initial starting value for each drug. While this treatment of the data is appropriate for analysis of the salmeterol effect, as TMV never fell below the starting value for the duration of the experiment, it may underestimate the effects of the second treatments with albuterol and ipratropium because TMV had fallen below starting values by 6 h. Therefore, we recalculated the 6- to 12-h and the overall (0- to 12-h) AUC for albuterol, ipratropium, and vehicle using the respective 6-h TMV values as the new reference point. These adjusted values are presented in Table 3 . Using this analysis, there were subtle changes in results. The mean 6- to 12-h effect of albuterol was positive, and the corresponding values for ipratropium and vehicle were less negative than given in Table 2 and illustrated in Figure 2. Based on this analysis, there was no significant difference between the response to the two doses of albuterol or ipratropium (0- to 6-h and 6- to 12-h AUCs). The 6- to 12-h effect of albuterol was still different from vehicle (p < 0.05), but the significant effect of ipratropium vs vehicle was lost. Considering the total AUC, both salmeterol and albuterol remained different from vehicle (p < 0.05), whereas ipratropium was not. These findings are similar to those in Table 2. Finally, although there were large mean differences between the ß-adrenergics and ipratropium, the overall (0- to 12-h) difference was lost.


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  		Table 3. Adjusted Effects of Treatments on TMV in Sheep*

 
Figure 3 illustrates the effects of albuterol, salmeterol, and ipratropium on reversal of HNE-induced depression in TMV. Both salmeterol and albuterol reversed (p < 0.05) the HNE-induced impairment in TMV (from 2.5 to 8 h), with no significant difference between the two ß-agonists. Ipratropium had no effect on the HNE-induced dysfunction (Fig 3).



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  		Figure 3. Treatment (upward arrows) with salmeterol (42 µg) and albuterol (180 µg) 2 h after HNE challenge reversed the HNE-induced fall in TMV. Neither ipratropium (36 µg) nor placebo affected the HNE-induced depression in TMV. There was no difference between the salmeterol and albuterol treatment arms, but both were significantly (p < 0.05) different from ipratropium and vehicle. TMV values are expressed as a percentage of the starting TMV value and are mean ± SE for six sheep.

 
We repeated this study with albuterol and salmeterol but extended the observation time to 12 h after treatment. In this experiment, the longer-lived action of salmeterol became apparent (Fig 4 ). Overall, there was a significant difference between the drugs over time (p < 0.005). These differences were apparent by 11 to 12 h after treatment, where the TMV values for the albuterol treatment arm were significantly lower than in the salmeterol treatment arm.



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  		Figure 4. Effect of salmeterol (42 µg) and albuterol (180 µg) treatment on HNE-induced fall in TMV. Extending the observation period from the experiments shown in Figure 3 demonstrated that the overall protection afforded by salmeterol was of greater duration than that seen with albuterol (two-way, repeated-measures analysis of variance, p < 0.05). Significantly different time points are identified (*p < 0.05 vs albuterol). TMV values are expressed as a percentage of the starting TMV value. Values are mean ± SE for four sheep.

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
The findings of the present study confirm previous work demonstrating that ß-adrenergic agents can stimulate MCC in normal airways. Furthermore, we demonstrated that both ß-adrenergic agents were superior to the anticholinergic agent ipratropium in this regard. We also show that both albuterol and salmeterol, but not ipratropium, can reverse HNE-induced depression in TMV. Thus, in disease states that are characterized by increased elastase levels, ß-adrenergic agents may be more beneficial than anticholinergics in improving mucus clearance. Finally, we documented the expected increased duration of action of salmeterol, by showing that a single treatment provided effects for up to 12 h after treatment in both normal and HNE-challenged airways.

We used TMV as an index of MCC for these studies. While it can be argued that changes in TMV do not completely reflect what might be observed with whole-lung clearance, our previous studies79 have shown correlative directional changes between TMV and whole-lung clearance. These published data, in addition to our unpublished observations, which show that albuterol enhances whole-lung clearance in sheep, provide some support that the changes seen in the present study might be indicative of changes that would occur in whole-lung clearance. In terms of the present report, TMV provided certain methodologic advantages that were important for the end points of this study. These included the ability to interject treatments during extended periods of monitoring and the use of the reversal protocols to identify potential therapeutic benefit.1022

As seen in Figure 1, there was a steady decline in TMV from the beginning to the end of the study in the vehicle treatment arm (approximately 18%). This has been observed in a number of our studies and likely reflects a combination of drying and irritation of the airway despite our attempts to humidify the inspired air.789 Nevertheless, this decline was prevented by salmeterol, whereas neither albuterol nor ipratropium completely prevented this reduction in TMV.

Salmeterol is a highly lipophilic molecule that diffuses laterally through the cell membrane to the ß-receptor.23 This diffusion slows its onset of action, relative to albuterol or formoterol, another long-acting ß-agonist.524 The side chain of the molecule is anchored to an exocite domain of hydrophobic amino acids, and this configuration allows the head of the molecule to repeatedly engage and disengage the receptor active site accounting for its long duration of action.523 Figure 1 suggests that the response to salmeterol might be slightly slower than albuterol, but this effect was not supported statistically. Figure 1 does, however, demonstrate the prolonged action of salmeterol when compared to albuterol. Thus, the in vivo response of TMV to these agents is consistent with the mechanistic data obtained in vitro. Table 2 indicates that overall both salmeterol and albuterol showed significant improvement in TMV.

The findings given in Table 2 and illustrated in Figure 2 are based on using the initial starting TMV value as the reference point for the AUC calculations. While this analysis does not influence the salmeterol response, as TMV was maintained at or above starting values for the entire study, this was not the case with albuterol or ipratropium. Thus, our analysis using the initial starting value for AUC calculations could diminish the effects of the second doses of these agents. Therefore we recalculated the 6- to 12-h and overall (0- to 12-h) AUC values for albuterol, ipratropium, and vehicle. The most significant difference in these results (Table 3) is the relationship of the response to the second albuterol and ipratropium doses to the first. Using the initial TMV value as the reference, the AUC for the second albuterol treatment was significantly less than the first and that for ipratropium trended in that direction (Table 2). However, these differences vanished if the respective 6-h TMV values were used as the new reference. This observation is probably more important for albuterol, as the overall response was different from vehicle whereas the response for ipratropium was not. Furthermore, whether or not there is a true difference in the response between the two doses of albuterol needs to be addressed in future studies because a decreased second response could be suggestive of tachyphylaxis. If such an effect occurred, it could indicate that a more prolonged maintenance of MCC, as seen with salmeterol, might be more effective than the periodic increases in clearance obtained with multiple doses of albuterol.

While stimulation of normal MCC indicates that an agent may be useful in modifying impaired clearance associated with airway disease, it is important to demonstrate this effect directly. HNE is an important mediator in asthma, COPD, and CF, and disease severity has been linked to concentrations of HNE in the airways.13141516 In this study, we used inhaled HNE to depress TMV in an attempt to mimic these disease states and then attempted to reverse effects with the study drugs. We have used this model previously to identify potential therapeutic regimens that might be useful in disease states associated with mucociliary dysfunction.101122 We found that ipratropium did not affect the response to inhaled HNE, whereas the HNE-induced depression in TMV was reversed with both albuterol and salmeterol. Over the 6-h posttreatment period, both ß-adrenergic agents demonstrated comparable effects. Salmeterol demonstrated its superior duration of action, however, when the posttreatment observation period was extended to 12 h (Fig 4).

TMV reflects the functional interaction among the ciliated surface epithelium, the mucus layer, and the underlying periciliary fluid layer.125 Abnormalities in any of these areas can impact TMV. We did not dissect out the area(s) affected by the ß-adrenergics, but in vitro studies418212627 suggest potential mechanisms that could contribute to the beneficial effects seen in the present study. ß-Adrenergics have been reported to cause mucus secretion in some species but not all.26 However, it is unlikely that such an increase would be beneficial in our studies, especially in those where the elastase-induced effects were reversed. It has been well established that ß-adrenergics increase ciliary beat frequency primarily through stimulation of adenyl cyclase and increasing cyclic adenosine monophosphate levels.26 In a recent study, Piatti et al26 found that salmeterol induced ciliostimulation in nasal epithelial cells taken from patients with COPD and pneumonia well as in cells from healthy control subjects. These in vitro findings are consistent with our in vivo observations of salmeterol (and albuterol) on normal TMV and elastase-induced mucociliary dysfunction. ß-Agonists have also been suggested to stimulate chloride secretion and water flux in submucosal gland cells.4 Such an action could help maintain mucus hydration, an important contributor to maintaining normal MCC, especially following elastase challenge, which not only stimulates mucus secretion1827 but increases sodium channel activation and loss of airway surface liquid.21

Anticholinergic agents are mucoregulatory agents in that they can reduce mucus secretion.28 Agents such as atropine have been shown to impair MCC, although such impairment has not been observed with ipratropium. These same studies, however, have also failed to show any improvement in mucociliary function with ipratropium in either healthy subjects or diseased patients.293031 The results of our study mirror these clinical reports, although we did see a difference in TMV between the vehicle and ipatropium in the 6- to 12-h segment of the time course study (study 1). Even with this slight enhancement, however, the response to ipratropium was significantly weaker that seen with either salmeterol or albuterol. Likewise ipratropium did not modify the HNE-induced depression in TMV. This would argue that the elastase-induced effect seen in the present study may not have a cholinergic component, which would be consistent with the sodium channel activation hypothesis noted above,21 or if there is a cholinergic component, ipratropium was administered at a dose that was insufficient to antagonize the effect.

In summary, we have shown that both short- and long-acting ß-agonists, when compared to the anticholinergic agent ipratropium, improve mucociliary function in both normal and experimentally impaired airways. As expected, the long-acting ß-adrenergic agent salmeterol showed increased duration of action under both conditions. Our results are consistent with the clinical data showing stimulatory effects of ß-adrenergics on MCC in normal subjects and patients with asthma, COPD, and CF. Further clinical comparisons will be necessary to determine if these long-acting agents provide an added treatment benefit for diseased patients.


   Footnotes
 
Abbreviations: AUC = area under the curve; CF = cystic fibrosis; HNE = human neutrophil elastase; MCC = mucociliary clearance; MDI = metered-dose inhaler; TMV = tracheal mucus velocity

This work was supported by a grant from GlaxoSmithKline.

Received for publication April 28, 2005. Accepted for publication June 15, 2005.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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