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J Appl Physiol 102: 2172-2178, 2007. First published March 8, 2007; doi:10.1152/japplphysiol.01300.2006
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Genetic variation of the beta2-adrenergic receptor is associated with differences in lung fluid accumulation in humans

Eric M. Snyder,1 Kenneth C. Beck,1 Stephen T. Turner,1 Eric A. Hoffman,3 Michael J. Joyner,2 and Bruce D. Johnson1

Departments of 1Internal Medicine and 2Anesthesiology, Mayo Clinic, Rochester, Minnesota; and the 3Division of Physiological Imaging, University of Iowa, Iowa City, Iowa

Submitted 16 November 2006 ; accepted in final form 5 March 2007


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 GRANTS
 ACKNOWLEDGMENTS
 REFERENCES
 
The beta2-adrenergic receptors (beta2AR) play an important role in lung fluid regulation. Previous research has suggested that subjects homozygous for arginine at amino acid 16 of the beta2AR (Arg16) may have attenuated receptor function relative to subjects homozygous for glycine at the same amino acid (Gly16). We sought to determine if the Arg16Gly polymorphism of the beta2AR influenced lung fluid balance in response to rapid saline infusion. We hypothesized that subjects homozygous for Arg at amino acid 16 (n = 14) would have greater lung fluid accumulation compared with those homozygous for Gly (n = 15) following a rapid intravenous infusion of isotonic saline (30 ml/kg over 17 min). Changes in lung fluid were determined using measures of lung density and tissue volume (computerized tomography imaging) and measures of pulmonary capillary blood volume (Vc) and alveolar-capillary conductance (DM, determined from the simultaneous assessment of the diffusing capacities of the lungs for carbon monoxide and nitric oxide). The saline infusion resulted in elevated catecholamines in both genotype groups (Arg16 283 ± 117% vs. Gly16 252 ± 118%, P > 0.05). The Arg16 group had a larger decrease in DM and increase in lung tissue volume and lung water after saline infusion relative to the Gly16 group (DM –13 ± 14 vs. 0 ± 26%, P < 0.05; lung tissue volume 13 ± 11 vs. 3 ± 11% and lung water +90 ± 66 vs. +48 ± 144 ml, P = 0.10, P < 0.05, for Arg vs. Gly16, respectively, means ± SD). These data suggest that subjects homozygous for Arg at amino acid 16 of the beta2AR have a greater susceptibility for lung fluid accumulation relative to subjects homozygous for Gly at this position.

pulmonary edema

THERE IS A CONSTANT fluid flux in the lungs between the pulmonary capillaries, interstitial space, pulmonary lymphatics, and the alveoli, with an estimated 3.8 ml/kg of total lung water in the normal human lungs (49). Although there appears to be a constant exchange of small amounts of fluid across the alveoli, the alveolar air space must remain relatively free of fluid in order for adequate gas exchange to occur (18). There are multiple clinical and environmental conditions that may cause alterations in normal lung fluid balance. These include conditions such as congestive heart failure (CHF), where there is evidence that a low-level subclinical pulmonary edema may exist, even in stable, well-managed patients (1, 17). Pulmonary edema may also occur at high altitude, where the onset of edema often becomes clinically significant after ~24 h of exposure (14, 39). With time, conditions such as CHF and exposure to altitude are contributory to changes in lung fluid balance; however, not all patients with CHF or all sojourners to altitude develop pulmonary edema. This heterogeneity may be related to variability in genes involved in lung fluid regulation.

Fluid flux between the pulmonary capillaries, interstitial space, and lymphatics follows the forces described by Starling (46). If the hydrostatic pressure of the pulmonary capillaries is greater than the hydrostatic pressure of the interstitium, there will be an increased fluid transfer into the interstitial space. Lymph flow acts to remove fluid from the interstitial space, which reduces the interstitial hydrostatic pressure and, therefore, plays an important role in preventing excessive alveolar fluid accumulation (22). Fluid in the alveoli can increase if interstitial fluid accumulation becomes greater than interstitial removal. In addition to these factors regulating lung water, epithelial sodium channels (ENaC) on the apical portion of type II alveolar cells serve to actively clear fluid from the alveoli (13, 27, 32). Patients with pseudohypoaldosteronism, a loss-of-function mutation of ENaCs, have been shown to have greater levels of lung water compared with normal subjects, highlighting the importance of these channels in lung fluid clearance even in individuals without CHF and at sea level (18).

The beta2ARs are found throughout the lung, in the airways, the pulmonary vasculature, and the pulmonary lymphatics and have been shown to play a key role in lung fluid balance (28). Stimulation of the beta2AR causes an increase in cAMP and protein kinase A (PKA), which leads to an increase in the number of ENaCs on the apical portion of type-II alveolar cells, and the probability of an open ENaC (3a). It is also likely that beta2AR stimulation results in an increase in Na+-K+-ATPase activity on the basolateral portion of type-II alveolar cells through an increase in PKA (2, 27). In addition, beta2AR stimulation leads to smooth muscle relaxation of the pulmonary lymphatics, which also play a key role in lung fluid balance, particularly in preventing excessive interstitial fluid accumulation. Therefore, the stimulation of the beta2ARs can prevent excessive accumulation of fluid in the lungs through several key pathways: 1) relaxation of the pulmonary lymphatics, reducing the hydrostatic pressure of the interstitium; 2) increasing the number and activity of the ENaCs on the apical portion of alveolar cells; and 3) enhancing the activity of Na+-K+-ATPase on basolateral portion of these same cells. Highlighting the importance of these mechanisms, in vivo work has demonstrated that overexpression of the beta2AR induces fluid clearance from the lungs in mice (7, 9). In addition, beta-agonists (including circulating catecholamines) increase lung fluid clearance in animals and reduce clinical symptoms of high-altitude pulmonary edema in humans (20, 36).

The gene encoding the beta2AR has been sequenced, and common polymorphisms have been described, including a glycine (Gly) substitution for arginine (Arg) at amino acid 16. Although the most functional variant is an isoleucine substitution for threonine at amino acid 164, this occurs in only a small percentage of the population (23). Several previous studies have examined variation at amino acid 16 because of the frequency and functional importance of this polymorphism. Subjects homozygous for arginine of the beta2AR at amino acid 16 (Arg16) have been shown to have reduced receptor function compared with subjects homozygous for Gly at this amino acid (Gly16), even in the presence of basal levels of circulating catecholamines, suggesting that differences in receptor density, rather than differences in desensitization, may be driving this effect (4, 5, 8, 12, 40, 43, 45). It is likely, therefore, that genetic variation of this receptor at amino acid 16 might influence lung fluid clearance, particularly under conditions that cause elevations in catecholamines.

In the present study, we sought to determine if the Arg16Gly polymorphism of the beta2AR differentially influenced lung fluid balance in response to a rapid infusion of isotonic saline. Rapid intravenous saline infusion has previously been shown to reduce exercise capacity, challenge the ability of the lungs to regulate fluid, and result in airflow obstruction and increased airway responsiveness (19, 29, 31). We hypothesized that subjects homozygous for Arg at amino acid 16 would have greater lung fluid accumulation compared with subjects homozygous for Gly at this amino acid.


   METHODS
TOP
 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 GRANTS
 ACKNOWLEDGMENTS
 REFERENCES
 
Protocol

The protocol was reviewed and approved by the Mayo Clinic Institutional Review Board, all participants provided written informed consent before study, and all aspects of the study were performed according to the declaration of Helsinki. Twenty-nine nonsmoking healthy subjects agreed to participate in the study and had no exclusion criteria (cardiopulmonary abnormalities, pregnancy, inability to exercise). Before performing the main protocol, subjects underwent screening tests that included an incremental cycle ergometry test to exhaustion (to rule out cardiovascular abnormalities), a pulmonary function test to rule out pulmonary disease, a complete blood count (CBC, to rule out anemia) and, in women, a pregnancy test.

In addition to the screening visit, the study involved one separate visit to our laboratory for a rapid infusion of isotonic saline.

Saline Infusion

A rapid intravenous saline infusion was used to challenge the ability of the lungs to handle fluid (19). The subjects were required to report to our laboratory in a fasting state, and all infusions were performed between 0700 and 0900. An 18-gauge venous catheter was inserted into a prominent antecubital vein for the infusion and for blood sampling. Baseline measures of pulmonary capillary blood volume (Vc), alveolar-capillary conductance (DM), and computerized tomography (CT) -based lung density and tissue volume were obtained before the infusion. Saline was then infused intravenously (30 ml/kg over ~15 min) while the subject was on the CT bed to optimize timing for postsaline CT measures. During the saline infusion, oxygen saturation (SaO2), blood pressure, heart rate (HR), and physical symptoms were continuously monitored and recorded every 2 min. Catecholamines (epinephrine and norepinephrine) were sampled pre- and immediately postsaline from the venous catheter. Following the infusion, repeat assessment of Vc, DM, lung density, and tissue volume were performed.

Data Collection

beta2AR genotyping.   beta2AR genotyping was PCR based according to methods of Bray et al. (3). Buffy coat, obtained from whole blood collected on EDTA, was extracted using the Gentra Pure gene DNA Isolation kit. Following extraction, DNA was treated with a proteinase K solution in preparation for PCR. The PCR reaction was conducted according to standard methods, using the following primer sequences (for Arg16Gly): forward 5'-AGC CAG TGC GCT TAC CTG CCA GAC-3' (at –32) and reverse 3'-CA TGG GTA CGC GGC CTG GTG CTG CAG TGC -5', resulting in a PCR product 107 base pairs in length. The Arg16 subjects are represented by a single 107-bp band and the Gly16 subjects by 82- and 25-bp bands. For Gln27Glu, the following primer sequences were used: forward 5'-CCC AGC CAG TGC GCT TAC CT-3' and reverse 3'-CCG TCT GCA GAC GCT CGA AC-5', resulting in PCR products 178 and 56 bp in length.

Catecholamines.   Venous catecholamines (epinephrine and norepinephrine) were assessed in the Mayo Clinic GCRC immunochemical core laboratory according to the methods of Sealey (38).

Measures of Vc and DM.   Measurement of Vc and DM has previously required the use of at least two, but preferably three, oxygen tensions. Recently, Tamhane et al. (47) have found that measuring the disappearance of nitric oxide (NO) in concert with carbon monoxide (CO) provides an accurate assessment of Vc and DM using just one oxygen tension. Triplicate maneuvers of the diffusing capacity of the lungs for carbon monoxide (DLCO) and nitric oxide (DLNO) were performed before saline and after saline.

DLCO and DLNO were assessed using the rebreathing technique with gases sampled on a mass spectrometer (Perkin-Elmer, 1100) and NO analyzer (Sievers Instruments, Boulder, CO) using custom analysis software. A 5-liter rebreathe bag was filled with 0.3% carbon monoxide (C18O), 40 parts per million (ppm) NO (diluted immediately before the test in the bag from an 800-ppm gas mixture), and O2. C18O was used instead of the more common C16O as the test gas because the mass spectrometer cannot distinguish C16O from N2 (because of similar molecular weights). The volume of gas used to fill the rebreathe bag was determined by the tidal volume of the subject. Consistent bag volumes were ensured using a timed switching circuit that, given a consistent flow rate from the tank, resulted in the desired volume (16). The switching circuit and tank were checked before each test for accurate volumes. At the end of a normal expiration [end-expiratory lung volume (EELV)], the subjects were switched into the rebreathe bag and instructed to nearly empty the bag with each breath for 10 consecutive breaths. The respiratory rate during the rebreathe maneuver was controlled at 32 breaths/min with a metronome. Following each diffusing capacity maneuver, the rebreathe bag was emptied with a suction device and refilled immediately before the next maneuver. For our laboratory, the coefficients of variation are 4.1% for the DLCO measure, 8.3% for the DLNO measures, 7.2% for DM, and 6.4% for Vc.

Measures of CT-based lung tissue volume and density.   All CT scans were performed on the same scanner (GE LiteSpeed spiral CT scanner, GE Healthcare). Initial slices were obtained for all scans and were 2.5 mm thick with a 1.2-mm overlap and then reconstructed to 1.25 mm with a 0.6-mm overlap. Before the baseline scan, a scout scan was performed to determine the location and size of the lungs. Marks were placed on the skin of the subject to indicate the anatomic location of the start of the scan, and the table height was recorded to ensure consistency with postsaline scans. The number of slices of the baseline scans was recorded to have consistent scans throughout the study.

Normalization of Lung Volumes During Scanning

Subjects were asked to breathe on a mouthpiece connected to a pneumotachometer, which was integrated with a portable computer with custom analysis software to provide accurate lung volumes during the scans. During the scans, the investigators observed the breathing pattern of each subject with the pneumotachometer and instructed the subjects to the desired lung volume for the breath-hold for imaging. The system was calibrated using a 3-liter syringe before each CT visit. For the baseline scans, subjects were asked to hold their breath at two lung volumes, total lung capacity (TLC) and EELV. The postsaline scans were performed at end-inspiratory lung volume. To obtain consistent lung density data while controlling for lung volume, the image data obtained postsaline was compared with values obtained by interpolating between the images obtained at TLC and EELV during baseline scanning. This scanning strategy was performed to ensure accurate comparisons because it is impossible to exactly match baseline and post-rapid saline infusion lung volumes, while minimizing the number of scans and amount of radiation exposure to the subjects.

Lung Density and Tissue Volume Analysis Using CT

The CT images were submitted for analysis using custom image analysis software [Pulmonary Analysis Software Suite (PASS), Physiological Imaging Laboratory, University of Iowa, Iowa City IA]. Using all of the slices from a subject's scan, the software first segmented the images to separate lung tissue from surrounding structures and the mediastinum as described previously (42). In each picture element, lung density was assumed to be a linear combination of air [Hounsfield units (HU) = –1,000] and lung tissue, which has density of water (HU = 0). Thus HU of –600 and –400 would represent 40% and 60% tissue, respectively. A histogram analysis of picture elements within the lung tissue was performed to obtained mean lung density in HU and tissue volume by summation among all elements in the lung fields. Lung tissue volume and lung density data obtained from baseline images were plotted against lung volume to be used for linear interpolation to obtain data against which other images were compared.

Estimation of Lung Water

Tissue volume as assessed by CT includes lung tissue, blood, and water. Saline infusion likely causes changes in lung blood volume and water volume but will minimally affect the volume of lung tissue. By combining our measures of tissue volume and Vc obtained from the lung diffusing capacity tests, we were able to estimate changes in lung water from baseline to postsaline using the following equation

Formula
where TVPst is the given tissue volume from the CT scan postintervention (in ml); TVIP is the interpolated tissue volume at the postintervention lung volume (in ml) from baseline CT scans; and VcPst and VcIP are the Vc (in ml) at postintervention and at baseline time points, respectively.

Data Analysis

All statistical comparisons were made using the SPSS statistical software package (Chicago, IL). Group demographics were compared using an independent samples t-test with an {alpha} level of 0.05 to determine significance. The changes in the physiological parameters, pulmonary function, catecholamines, DLCO, DM, Vc, tissue volume, and lung water in response to saline infusion were compared using a repeated-measures ANOVA with an {alpha} level of 0.05 to determine significance. The differences in the physiological parameters, pulmonary function, catecholamines, DLCO, DM, Vc, tissue volume and lung water between the genotype groups at baseline and postsaline were compared using an independent-samples t-test with an {alpha} level of 0.05 to determine significance. A Levene's test was performed before each comparison to determine equality of variance. Values are means ± SD.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 GRANTS
 ACKNOWLEDGMENTS
 REFERENCES
 
Subject Characteristics

Twenty-nine subjects [Arg16 n = 14 (4 females); Gly16 n = 15 (3 females)] who had no exclusion criteria (cardiopulmonary abnormalities, inability to exercise, use of cardiovascular or pulmonary medications) participated in the study. There were no differences between genotype groups in age, weight, body mass index (BMI), or peak oxygen uptake (VO2 peak) [age 30 ± 7 vs. 30 ± 8 yr, weight 76 ± 15 vs. 82 ± 11 kg, BMI 25 ± 4 vs. 25 ± 4 kg/m2, VO2 peak 37 ± 7 vs. 40 ± 7 ml·kg–1·min–1 (103 ± 15 vs. 105 ± 11% predicted) for Arg16 vs. Gly16], but the Gly16 group was taller than the Arg16 group (174 ± 7 vs. 181 ± 8 cm for Arg16 and Gly16, respectively).

Saline Infusion

On average, 2,210 ml of saline was infused in the Arg16 group, while 2,380 ml was infused in the Gly16 group (over 17 min for both groups). The most common symptom reported during the saline infusion was a chest tightness that averaged 1.7 on a scale of 0 to 4. Saline infusion caused a similar increase in HR in both groups (Arg16 = 25 ± 7%, Gly16 = 18 ± 5% change from baseline, P > 0.05), but there were no changes in SaO2. There were increases from baseline in epinephrine and norepinephrine, with no differences between genotype groups (epinephrine 283 ± 117% vs. 252 ± 118% and norepinephrine 129 ± 137% vs. 99 ± 123% for the Arg16 and Gly16 groups, respectively) (Fig. 1). The Arg16 group had greater decreases in DM compared with the Gly16 group (Fig. 2). DM corrected for Vc fell more in the Arg16 group compared with the Gly16 group (Fig. 3). This condition also resulted in increases in lung tissue volume, density, and estimates of lung water in both groups, with the greatest increase in lung water in the Arg16 group (lung water = 90 ± 66 ml vs. 48 ± 144 ml, P < 0.05) (Table 1).


Figure 1
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  		Fig. 1. Changes in catecholamines [epinephrine (top) and norepinephrine (bottom)] following saline infusion according to genotype. {dagger}P < 0.05 compared with baseline.

 

Figure 2
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  		Fig. 2. Change in diffusing capacity of the lungs for carbon monoxide (DLCO) and components following saline infusion according to genotype. Vc, pulmonary capillary blood volume; DM, alveolar-capillary conductance. *P < 0.05, Arg16 vs. Gly16.

 

Figure 3
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  		Fig. 3. Change in alveolar-capillary conductance corrected for pulmonary capillary blood volume (DM/Vc) in response to saline infusion. The dashed line with open diamonds represents the Arg16 group, while solid line with filled squares represents the Gly16 group. *P < 0.05 Arg16 vs. Gly16.

 

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  		Table 1. Changes in lung tissue volume (from computed tomography) and estimated lung water following saline infusion according to genotype

 

   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
GRANTS
 ACKNOWLEDGMENTS
 REFERENCES
 
This study suggests that subjects homozygous for the Arg allele at amino acid 16 of the beta2AR have an increase in lung fluid accumulation relative to subjects homozygous for Gly at this position during an intervention that has previously been shown to challenge the ability of the lungs to regulate fluid. This is evident since the Arg16 subjects had lower conductance of the alveolar-capillary membrane, and higher lung tissue volume and estimates of lung water following saline infusion relative to the Gly16 subjects.

Lung Fluid Balance

While it is established that certain clinical and environmental conditions can cause alterations in lung fluid balance and lead to alveolar fluid accumulation, less is clear about the amount of alveolar fluid in the healthy normal lung (1, 14, 17, 39). Evidence of lung fluid flux into the alveoli even in healthy subjects has been demonstrated by Kerem et al. (18), who reported that subjects with pseudohypoaldosteronism (a loss-of-function mutation of the ENaCs) have more lung fluid than those without this mutation. Because the ENaCs influence lung fluid clearance from the air space, this study suggests that fluid must transfer into the air space in humans even with normal pulmonary vascular resistance and pulmonary capillary integrity. The ENaCs have been localized to type-II alveolar cells and play a key role in alveolar fluid clearance allowing for Na+ and water transfer from the alveolar space into the cell and are primarily regulated by the beta2ARs (13, 32).

beta2ARs and Lung Fluid Clearance

Several studies have shown the importance of the beta2ARs in lung fluid regulation (7, 11, 26, 30). Immediately following birth, stimulation of the beta2ARs clear amniotic fluid from the lungs, stimulated by circulating epinephrine (10). Additionally, the beta2ARs clear fluid from the lung following acute lung injury and sepsis and have been shown to reduce the clinical and radiographic signs of high-altitude pulmonary edema in adults (11, 36, 37, 48). Animal models have suggested that stimulation of the beta2ARs in the lung stimulates lung fluid clearance even in healthy animals (7, 34). The beta2ARs have been localized to lymphatic smooth muscle tissue, and stimulation of these receptors on the pulmonary lymphatics leads to smooth muscle relaxation, dilation of the lymphatic vessels, and movement of water away from lungs (15, 24, 50). It is possible, therefore, that the observed differences between the genotype groups in lung fluid accumulation in the present study were a result of dilation of the pulmonary lymphatics and a concurrent increase in lung lymph flow, reducing the hydrostatic pressure of the interstitium.

Limitations

A potential limitation to studying alterations in lung fluid balance in humans is the difficulty assessing small changes in lung water. We have used state-of-the art methods combining CT imaging at controlled lung volumes (anatomic assessment) and measures of gas transfer (DLCO and DLNO; physiological assessment) to estimate changes in lung water in healthy humans. Both of these independent measures demonstrated the consistent findings that rapid saline infusion resulted in lung fluid accumulation characterized by an increase in lung density and a widening of the alveolar-capillary membrane, even when corrected for changes in Vc. A limitation of CT scanning is the inability to separate blood from tissue and water (because of similar HUs). Therefore, in the present study, we calculated the estimated changes in lung water by combining tissue volume from CT scanning with Vc measured from the DLCO-DLNO technique. Because Vc only measures the amount of blood that is in contact with the alveoli, it is possible that this is not a true representation of the amount of blood in the entire lung. We did simultaneously measure cardiac output [reported in (45)] and found that the Gly16 subjects had a higher cardiac output both before and following the saline infusion. Because essentially all of the blood from the heart goes to the lungs, and because we found a lower tissue volume and lung density in the Gly16 group, it is possible that we underestimated the difference in lung water between the genotype groups.

In the present study, we sought to determine differences in lung fluid balance on the basis of genetic variation of the beta2AR at amino acid 16. Although the interest in the phenotypic effects of single-nucleotide polymorphisms is considered by some to have less of an impact than haplotype analysis, genetic variation of the beta2AR at amino acid 16 appears to have powerful physiological and clinical implications (8, 12, 21, 40, 41, 43–45). Another polymorphism of this protein that is frequently studied and suggested to have an effect on receptor function is amino acid 27. There is significant linkage disequilibrium between amino acids 16 and 27; therefore, when the two polymorphisms are combined, they are important predictors of the variation along the rest of the beta2AR gene (6). On this basis, we provide data on several of our indexes of lung water according to variation at amino acids 16 and 27 (Table 2). Although not powered for statistical analysis of amino acid 27, there appears to be a primary effect at amino acid 16, with a secondary effect at position 27. Although it will be important in future studies to consider variation at multiple sites with larger groups, smaller mechanistic studies are essential to understanding mechanisms behind larger, population-based, less mechanistic studies (21).


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  		Table 2. Changes in lung diffusing capacity, density, and tissue volume with rapid saline infusion according to genetic variation at amino acids 16 and 27

 
It is not possible from the present study design to determine the contribution of lung fluid accumulation vs. active fluid clearance to the observed genotype-related differences in lung water. To determine if there are differences between the genotype groups in active fluid clearance, a minimum of two separate time points measuring differences in lung water would have been necessary. Previous work has demonstrated that basal alveolar fluid clearance is approximately 8–12% over 4 h in humans and increases to 14–28% in the presence of terbutaline or catecholamines (33, 35). In the present study, the infusion time averaged 17 min, the final CT scan was taken at minute 21 and the DLCO and DLNO measures were taken at minute 30 (given the transit time to the physiological core laboratory). In addition, there was a significant elevation in venous epinephrine that likely accelerated alveolar fluid clearance (25). We feel, therefore, that the genotype-related differences in lung water are most likely explained primarily by beta2-mediated changes in the lymph flow from the lung and active fluid clearance from the alveolar air space.

Implications

Lung fluid regulation is challenged in a number of clinical and environmental conditions. Patients with heart failure and individuals who travel to high altitude may be particularly susceptible to pulmonary edema; however, not all patients with heart failure or all sojourners to high-altitude develop pulmonary edema despite similar clinical or environmental conditions. This would suggest that genetic variation in the regulatory proteins important in lung fluid balance may influence the susceptibility to pulmonary edema. Although the pulmonary edema that occurs in heart failure and with exposure to high altitude develops over a longer time period than that which was used in the present study, it is likely that similar mechanisms involved in regulating lung fluid are challenged in these conditions. The results of the present study suggest that subjects homozygous for Arg at amino acid 16 of the beta2AR demonstrate greater lung fluid accumulation compared with subjects homozygous for Gly following rapid fluid loading. Future, larger studies are needed in patients with heart failure or in sojourners to high altitude where prolonged elevations in catecholamines may accentuate the differences between genotype groups due to a proposed enhanced susceptibility to receptor desensitization in the Arg16 subjects.


   GRANTS
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
ACKNOWLEDGMENTS
 REFERENCES
 
This work was supported by National Heart, Lung, and Blood Institute Grants HL-71478 and HL-63328, as well as American Heart Association Grant 56051Z. The Mayo Clinic GCRC is supported by National Institutes of Health Grant M01-RR-00585.


   ACKNOWLEDGMENTS
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 ACKNOWLEDGMENTS
REFERENCES
 
We thank Kathy O'Malley, Angela Heydman, and Minelle Hulsebus for help with data collection, Jodie Van De Rostyne and Pamela Hammond for help with genotyping and sample management, and Renee Blumers for help with manuscript preparation, as well as the efforts of the study participants. We also thank the staff of the General Clinical Research Center (GCRC) for assistance throughout this study.


   FOOTNOTES
 

Address for reprint requests and other correspondence: E. M. Snyder, Div. of Cardiovascular Diseases, Mayo Clinic College of Medicine, 200 1st St., SW, Rochester, MN 55905 (e-mail: snyder.eric{at}mayo.edu)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
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 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 ACKNOWLEDGMENTS
 REFERENCES
 

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