Effects of Therapeutic Doses of Albuterol on β 2 -Adrenergic Receptor...

Journal of Asthma 38(1) 59ndash64 (2001)

Effects of Therapeutic Doses of Albuterolon β2-Adrenergic Receptor Densityand Metabolic Changes

Michael I Anstead MD Travis A HuntJohn W McConnell Jr MD andNausherwan K Burki MD PhD

Division of Pulmonary and Critical Care Medicine University of KentuckyMedical Center Lexington Kentucky

ABSTRACT

β2-Agonist drugs at inhaled supratherapeutic doses or when given orally or parenter-ally alter peripheral lymphocyte β2-adrenoceptor density (βAR) and have demon-strable metabolic effects However it is not known whether these changes occur attherapeutic inhaled doses We therefore studied the effects of therapeutic doses of in-haled albuterol in five asthmatic subjects (mean age 230 plusmn 24 years) and six normalsubjects (mean age 283 plusmn 33 years) Subjects were studied in a randomized double-blind protocol in which each subject received either inhaled albuterol (270 microg fourtimes daily) for 2 weeks followed by placebo or vice versa in two sequential 2-weekperiods separated by a 2-week washout period In the asthmatics baseline FEV1

increased significantly (p lt 005) after 2 weeks of inhaled albuterol treatment com-pared to the initial visit and after 2 weeks of placebo (mean FEV1 32 L plusmn 07 L29 L plusmn 05 L and 30 L plusmn 07 L respectively) Baseline peripheral lymphocyte βARwas not significantly different (p gt 005) between the asthmatic (mean 757 plusmn 176)and normal subjects (mean 732 plusmn 251) However in neither group was there anysignificant change (p gt 005) in βAR or plasma potassium insulin or glucose eitheracutely or after 2 weeks of albuterol therapy The present study confirms that there isno difference in peripheral lymphocyte βAR between asthmatic and normal subjectsand also shows that at therapeutic doses of inhaled albuterol there are no significantchanges in βAR or metabolic effects

Address correspondence to NK Burki MD PhD FCCP Division of Pulmonary and Critical Care University of KentuckyMedical Center MN614 800 Rose Street Lexington KY 40536 Fax 1-859-323-1020

59

Copyright Ccopy 2001 by Marcel Dekker Inc wwwdekkercom

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60 Anstead et al

KEY WORDS β2-Agonists β2-Adrenoceptors Asthma Plasma potassium

INTRODUCTION

β2-Agonist drugs are widely used in the treatment ofasthma as bronchodilator drugs they act by stimulation ofβ2-adrenoreceptors on airway smooth muscle The mostcommon standard route of administration is by inhalationHowever studies that have examined the direct effectsof these drugs on β2-adrenoreceptor function have usu-ally utilized either supratherapeutic inhaled doses or oralor parenteral doses (1ndash3) These drugs are also knownto have metabolic effectsmdashhypokalemia hyperglycemiaand hyperinsulinemiamdashthat are also mediated by β2-adrenoreceptor stimulation (45) Again most previousstudies of the metabolic effects have examined eithersupratherapeutic inhaled doses or parenteral or oral reg-imens (6ndash8) and the effects of standard therapeutic in-haled doses on the correlation between the bronchodilatorand metabolic effects of β2-agonists have not been syste-matically studied Furthermore there have been no studiesexamining the correlation between the metabolic effectsof β2-agonists and their effect on peripheral lymphocyteβ2-adrenoreceptor density

Therefore it is not known whether at therapeutic in-haled doses of β2-agonists bronchodilation occurs in asth-matics in the absence of metabolic effects and whetherthere are significant effects on peripheral lymphocyte β2-adrenoreceptor density We therefore designed this studyto examine the acute and chronic effects of standard dosesof an inhaled β2-agonist albuterol on bronchodilatationand peripheral blood lymphocyte β2-adrenergic receptordensity as well as on plasma potassium glucose and in-sulin in asthmatics and normal subjects

METHODS

A double-blind placebo-controlled crossover studywas performed in 11 nonsmoking subjects six normals(five males one female mean age = 283 plusmn 24 years)and five stable asthmatics (two males three females meanage = 230 plusmn 33 years) Written informed consent wasobtained from all subjects

All subjects had a complete medical history and exam-ination performed followed by spirometry at baseline andafter two puffs (90 microgpuff) of albuterol from a metereddose inhaler (MDI) Bronchodilator responsiveness wasdefined as an increase in FEV1 of at least 15 from base-line The asthmatic subjects were selected on the basis of

a history of asthma absence of any other systemic disor-der and documented responsiveness to inhaled albuterolNo subject had received inhaled or systemic steroids mastcell stabilizers or β2-agonists for at least 30 days beforeinitiation of the study The asthmatic subjects were al-lowed to use inhaled ipatroprium bromide for increasedasthma symptoms for the month before and during thestudy

The study was performed in two sequential treatmentperiods of 2 weeks each separated by a 2-week washoutperiod with each subject receiving inhaled albuterol threepuffs (90 microgpuff) four times a day from an MDI in oneof the 2-week treatment periods and inhaled placebo inthe other The sequence of drug vs placebo during thetwo treatment periods was based on a blind randomizedprotocol

Each subject attended the laboratory at the beginningand end of each 2-week period for a total of four vis-its After an overnight fast and having abstained fromcaffeine for a 12-hour period before each visit baselineblood samples were drawn at approximately the sametime of day (900 AM) on each occasion Blood sampleswere also drawn at 10 30 and 240 minutes after drug orplacebo administration Peripheral blood lymphocyte β2-adrenergic receptor density was measured on the baselineand 240-minute samples and plasma glucose potassiumand insulin were measured on all samples Spirometrywas performed by standard techniques (9) for measure-ment of FEV1 and FVC at baseline and at 10 30 and240 minutes

β2-Adrenergic receptor density on lymphocytes wasdetermined by Broddersquos technique (10) as described pre-viously (11) Lymphocytes were isolated from 40 mL ofblood by density gradient centrifugation with 12 mL ofFicoll-Paque and 25 mL of Hanks solution This was cen-trifuged at 400 G for 35 minutes at 4C The pellet was ag-itated with fresh Hanks solution to obtain a homogeneousmixture and an aliquot was counted on an automatedblood counter (Coulter S+IV Coulter Rcopy Instruments) Theisolation procedure took 3ndash4 hours and yielded a prepara-tion of 80ndash90 lymphocytes confirmed by microscopicidentification

Triplicate samples of 5 times 105 lymphocytes were in-cubated with eight concentrations of [125I]-(-) iodopin-dolol from 25 to 150 pM for 24 hours at 4C Nonspe-cific binding was determined using isoproterenol at a highconcentration (10 microM) to displace the receptor-boundligand The reaction was terminated by adding 10 mL of

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β2-Agonists and β2-Adrenoceptors 61

Table 1

Spirometry and β-Adrenergic Receptor Densities (βAR) in Normal and Asthmatic Subjects (Mean plusmn SD)

After 2 Weeks After 2 WeeksInitial Visit Initial Visit of Place Treatment of Albuterol Treatment

Baseline Post-Placebo Baseline Post-Albuterol Baseline Post-Placebo Baseline Post-Albuterol

Normal FEV1 L 45 plusmn 07 46 plusmn 07 44 plusmn 08 46 plusmn 07 45 plusmn 08 46 plusmn 07 46 plusmn 08 47 plusmn 09subjects

n = 6 βAR 827 plusmn 175 838 plusmn 176 732 plusmn 251 680 plusmn 360 775 plusmn 185 765 plusmn 204 763 plusmn 258 845 plusmn 189Asthmatics FEV1 L 30 plusmn 08b 33 plusmn 10 29 plusmn 05b 36 plusmn 07a 30 plusmn 07b 31 plusmn 07 32 plusmn 06bc 37 plusmn 06a

n = 5 βAR 763 plusmn 163 607 plusmn 151 757 plusmn 176 642 plusmn 89 641 plusmn 141 686 plusmn 159 660 plusmn 114 780 plusmn 243

a Significantly (p lt 005) different from baseline paired t-testb Significantly (p lt 005) different from normal subjects unpaired t-testc Significantly (p lt 005) different from baselines at initial visits and after 2 weeks of placebo treatment one-way repeated measures ANOVA

10-mM Tris Hcl 154-mM NaCl buffer pH 74 and fil-tration over Whatman CFC filters (Whatman Inc) Eachfilter was then washed with 10 mL of buffer and countedon a gamma counter (Compugamma 1282 LKB Wallac)Specific-binding of [125I]-(-) iodopindolol was defined astotal minus nonspecific binding A computer program(Ligand Rcopy Biosoft Company) was utilized to determinethe maximum binding capacity (Bmax) for each subject

The mean coefficient of variation of repeated estimatesof βAR in individual samples as previously determinedin our laboratory is 98 (11) The data were analyzedfor significance of change within and between groups byrepeated measures ANOVA (12)

Table 2

Plasma Values at Baseline and Following Inhaled Albuterol or Placebo in Normal(n = 6) and Asthmatic (n = 5) Subjects (Mean plusmn SD)

Subjects Parameter Baseline 10 min 30 min 240 min

Normal K+ (mEqL) Placebo 42 plusmn 02 43 plusmn 02 42 plusmn 02 41 plusmn 01Albuterol 40 plusmn 03 39 plusmn 03 40 plusmn 03 40 plusmn 04

Asthmatic Placebo 45 plusmn 13 46 plusmn 15 49 plusmn 17 47 plusmn 15Albuterol 43 plusmn 06 42 plusmn 07 42 plusmn 08 42 plusmn 05

Normal Glucose (mgdL) Placebo 779 plusmn 61 828 plusmn 65 839 plusmn 56 846 plusmn 110Albuterol 824 plusmn 194 855 plusmn 172 843 plusmn 58 768 plusmn 104


Normal Insulin (microUmL) Placebo 146 plusmn 117 143 plusmn 114 174 plusmn 158 185 plusmn 230Albuterol 131 plusmn 79 228 plusmn 179 228 plusmn 234 177 plusmn 127


There was no significant change (p gt 005 repeated measures ANOVA) in plasma K+ glucose or insulin after inhaledalbuterol or placebo in either group of subjects

RESULTS

As was expected baseline FEV1 was significantly(p lt 005) lower in the asthmatic subjects in whom therewas also a significant acute increase in FEV1 after in-haled albuterol (Table 1) After 2 weeks of albuterol ther-apy the baseline FEV1 in the asthmatics was significantly(p lt 005) increased Peripheral blood lymphocyte β2-adrenergic receptor density was not significantly differentat baseline between the two groups of subjects nor wasthere any significant effect of albuterol or placebo eitheracutely or following 2 weeks of treatment in either subjectgroup

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62 Anstead et al

There were no significant (p gt 005) changes inplasma K+ glucose or insulin in either group of sub-jects with exposure to inhaled albuterol or placebo norwere there significant differences between the two groupsin these parameters representative values from the initialvisits are shown in Table 2

DISCUSSION

The present study demonstrates that therapeutic dosesof inhaled albuterol a β2-agonist drug do not cause sig-nificant metabolic effects either acutely or with chronictreatment nor does it alter the density of β2-receptors oncirculating lymphocytes in asthmatic or normal subjects

Several studies have shown that when β2-agonists aregiven at supratherapeutic inhaled doses or by the par-enteral route they may cause significant metabolic ef-fects (6ndash813ndash16) in addition to their bronchodilator ac-tion Both the bronchodilator and the hypokalemic effectsare believed to result from stimulation of β2-receptorshowever the interrelationship between β2-receptor den-sity and the metabolic and bronchodilator effects isunknown

From currently available data it appears that β2-agonistdrugs cause bronchodilation by both cAMP-dependentand non-cAMP-dependent mechanisms (1718) althoughthe precise contribution of each pathway is unclear(1819) β2-Agonist drugs bind to β2-receptors on cellsand result in the intracellular generation of cAMP whichactivates protein kinase A (PKA) and causes smooth mus-cle relaxation recent data suggest that cAMP may also actby activation of protein kinase G (20) In addition a non-cAMP-mediated airway smooth muscle relaxant mecha-nism via a direct effect of β2-agonists on maxi-K channelsin smooth muscle has been described (17)

Previous studies on baseline β2-adrenoreceptor func-tion in asthmatics compared to normal subjects havereported either no difference or minor reductions inβ2-adrenoreceptor density but the consensus is thatdifferences if any are insignificant (18) and one post-mortem study (21) found no difference in airway β2-adrenoreceptor density in a patient with severe asthmacompared to subjects with normal lungs In the presentstudy care was taken to ensure an adequate washout pe-riod for β2-agonists in all subjects and the measurement ofβ2-adrenoreceptor density in our laboratory has good re-producibility (11) Our results indicate that in patients withmild asthma the baseline peripheral β2-adrenoreceptordensity is similar to that in normal subjects These dataare in accordance with the general view that baseline β2-

adrenoreceptor density in asthma is not different from thatin normal subjects (18)

Curiously there are few published studies in asthmaticsthat have examined β2-adrenoreceptor function in relationto therapeutic levels of β2-agonist therapy In normal hu-man subjects Hayes et al (3) using positron emissiontomography (PET) demonstrated a good correlation be-tween induced changes in peripheral β2-adrenoreceptordensity and changes in lung β2-adrenoreceptor densitythey also found that the percent change in lung β2-adrenoreceptor density was about half of the percentchange noted in peripheral β2-adrenoreceptor densityThus it would be reasonable to assume that the absence ofa significant change in peripheral β2-adrenoreceptor den-sity in the present study reflects a similar absence of signif-icant change inβ2-adrenoreceptor density in the lungs thatis that neither acute nor chronic therapeutic inhaled dosesof albuterol affect β2-adrenoreceptor density At first sightthese results appear to contradict previous studies that havefound a decrease in β2-adrenoreceptor density with acuteand chronic β2-agonist treatment However closer exam-ination of the previous data indicates that these changesin β2-adrenoreceptor density are seen either with oral orparenteral doses or with very high supratherapeutic in-haled doses of β2-agonists Thus studies with oral terbu-taline 15 mgday for 5 weeks found a significant decreasein peripheral β2-adrenoreceptor density but no change inairway bronchodilator responsiveness in asthmatic sub-jects (2) similar results were seen in normal subjects after2 weeks of treatment (22) On the other hand with inhaledalbuterol at therapeutic doses (800 microgday) Connolly et al(23) found no significant changes in β2-adrenoreceptordensity or in bronchodilator effectiveness after 4 weeks oftreatment Furthermore Hauk et al (24) did not note anydecrease in pulmonary β2-adrenoreceptor density in lunglobectomy specimens from patients treated with therapeu-tic doses of terbutaline prior to the operation Howeverstudies in normal subjects utilizing much higher doses ofinhaled β2-agonists have been able to demonstrate a de-crease in β2-adrenoreceptor density Turki et al (1) founda 70 decrease in β2-adrenoreceptor gene expressionfrom bronchial lavage-derived epithelial and mononuclearcells in normal subjects after 10 mg of inhaled metapro-terenol and Hayes et al (3) documented 42 and 22 de-creases in peripheral and lung β2-adrenoreceptor densityrespectively in normal subjects after 2 weeks of combinedoral (16 mgday) and inhaled (16 mgday) albuterol

It seems clear therefore from the present and previousdata that treatment with β-agonist drugs at optimal doselevels that cause clinically significant bronchodilation ineither acute or chronic treatment regimens does not alter

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β2-adrenoreceptor density The possibility remains thatwith longer duration of treatment andor a larger numberof study subjects the results may have been different how-ever this is unlikely given the findings of previous studies(23) as well as the strength of the statistical analysis inthe current study

The metabolic effects of β2-agonists are well describedand consist of hypokalemia hyperglycemia and an in-crease in plasma insulin (6) Hyperglycemia is due to thestimulation of glycogenolysis and gluconeogenesis (5)the increase in plasma insulin is believed to be either a re-sponse to the hyperglycemia or due to direct stimulationof pancreatic islet cells (5) Of specific relevance to thepresent study is the hypokalemia induced by β-agoniststhis is due to increased cellular uptake of K+ by activationof NaK ATPase by cAMP (4) It would be reasonableto assume that since β2-agonist-induced hypokalemia andbronchodilation are both cAMP mediated functions thetwo effects would be seen simultaneously in asthmaticswho are responsive to bronchodilators However our re-sults indicate that with therapeutic doses of inhaled al-buterol hypokalemia does not occur even with signifi-cant bronchodilation in asthmatics Previous studies ofthe metabolic effects of inhaled albuterol have found sim-ilar results Wong et al (14) compared increasing doses ofinhaled albuterol fenoterol and terbutaline in 10 asthmat-ics Their data show that at the lowest doses of these drugswhich were comparable to those in the present studythe degree of bronchodilation was similar to that in thepresent study and indeed near maximal They also foundno metabolic effects at this dose Similarly Crane et al(8) reported no hypokalemia in normal subjects at simi-lar inhaled doses of albuterol isoproterenol or fenoterolthey did not measure the degree of bronchodilation Theseresults would imply that either the bronchodilator actionof cAMP occurs at a much lower level than that at whichcAMP activates NaK ATPase or that at therapeutic in-haled doses of albuterol bronchodilation is induced by anon-cAMP-dependent mechanism Interestingly the ab-solute degree of bronchodilation induced by the inhaledalbuterol in the present study was very similar to that re-ported in our previous studies in which both hypokalemiaand bronchodilation were demonstrated simultaneously inreponse to β-agonist drugs For example Kung et al (6)and Clifton et al (7) demonstrated absolute mean FEV1

changes from baseline of 038 L and 03 L respectively(12 and 9 respectively) versus 06 L (21) in thepresent study Thus the lack of metabolic response inthe present study cannot be attributed to an insufficientbronchodilator dose but must be related to the differencein the drug delivery mode In the previous studies noted

above (67) intravenous terbutaline was used whereas inthe present study inhaled albuterol was used Furthermorethe difference in metabolic response cannot be attributedto differences between β2-agonist drugs since it has pre-viously been shown that the hypokalemic action of terbu-taline is less than that of albuterol when given by the sameroute (14)

In summary the present study confirms previous datashowing that there is no difference in peripheral β2-adrenoreceptor density between asthmatic and normalsubjects and demonstrated that at therapeutic doses of in-haled albuterol that resulted in significant bronchodilationin asthmatic subjects there were no significant metaboliceffects or changes in peripheral β2-adrenoreceptor densityeither acutely or after 2 weeks of treatment in normal orasthmatic subjects It is possible that at therapeutic dosesof inhaled β2-agonists bronchodilation is mediated by anon-cAMP-dependent mechanism

ACKNOWLEDGMENTS

Partly supported by a grant from The Jewish HospitalHeart-Lung Institute Louisville Kentucky

REFERENCES

1 Turki JS Green A Newman KB Myers MALiggett SB Human Lung Cell β2-Adrenergic Recep-tors Desensitises in Response to in Vivo Administered β-Agonist Am J Physiol (Lung Cell Mol Physiol 13) 1995269 L709ndashL714

2 Tashkin DP Conolly ME Deutsch RI Hui KKLittner M Scarpace P Abrass I Subsensitizationof Beta-Adrenoceptors in Airways and Lymphocytes ofHealthy and Asthmatic Subjects Am Rev Respir Dis1982 125 185ndash193

3 Hayes JH Qin F Rhodes CG et al In Vivo Quantifi-cation of Human Pulmonary β-Adrenoceptors Effect ofβ-Agonist Therapy Am J Respir Crit Care Med 1996154 1277ndash1283

4 Clausen T Flatman JA The Effect of Catecholamineson Na-K Transport and Membrane Potential in Rat SoleusMuscle J Physiol (Lond) 1977 270 383ndash414

5 Haffner CA Kendall MJ Metabolic Effects of β2-Agonists J Clin Pharm Ther 1992 17 155ndash164

6 Kung M White JR Burki NK The Effect of Subcu-taneously Administered Terbutaline on Serum Potassiumin Asymptomatic Adult Asthmatics Am Rev Respir Dis1984 129 329ndash332

7 Clifton GD Hunt B Patel RC Burki NK Effectsof Sequential Doses of Parenteral Terbutaline on Plasma

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64 Anstead et al

Levels of Potassium and Related Cardiopulmonary Re-sponses Am Rev Respir Dis 1990 141 575ndash579

8 Crane J Burgess C Beasley R Cardiovascular and Hy-pokalaemic Effects of Inhaled Salbutamol Fenoterol andIsoprenaline Thorax 1989 44 136ndash140

9 American Thoracic Society Lung Function Testing Selec-tion of Reference Values and Interpretative Strategies AmRev Respir Dis 1991 144 1202ndash1218

10 Brodde OE Brinkmann M Schmeuth R OrsquoHara NDaul A Terbutaline-Induced Desensitization of HumanLymphocyte β2-Adrenoceptors Accelerated Restorationof β-Adrenoceptor Responsiveness by Prednisone and Ke-totifen J Clin Invest 1985 76 1096ndash1101

11 Anstead MI Hunt TA Carlson SL Burki NK Vari-ability of Peripheral Blood Lymphocyte Beta-2-AdrenergicReceptor Density in Humans Am J Respir Crit CareMed 1998 157 990ndash992

12 Snedecor GW and Cochran WG Statistical Methods8th Ed Iowa State University Press Ames Iowa 1989217ndash236 329ndash331

13 Lipworth BJ Struthers AD McDevitt DG Tachyphy-laxis to Systemic but Not to Airway Responses DuringProlonged Therapy with High Dose Inhaled Salbutamol inAsthmatics Am Rev Respir Dis 1989 140 586ndash592

14 Wong CS Pavord ID Williams J Britton JRTattersfield AE Bronchodilator Cardiovascular and Hy-pokalemic effects of Fenoterol Salbutamol and Terbu-taline in Asthma Lancet 1990 336 1396ndash1399

15 Lipworth BJ McDevitt DG Struthers AD Electro-cardiographic Changes Induced by Inhaled Salbutamol Af-ter Treatment with Bendrofluozide Effect of ReplacementTherapy with Potassium Magnesium and TriamtereneClin Sci 1990 78 255ndash259

16 Rahman ARA McDevitt DG Struthers ADLipworth BJ Sex Differences in Hypokalemic and Elec-trocardiographic Effects of Inhaled Terbutaline Thorax1992 47 1056ndash1059

17 Kume H Hall IP Washabau RJ Takagi KKotlikoff MI Beta-Adrenergic Agonists Regulate KcaChannels in Airway Smooth Muscle by cAMP Dependentand -Independent Mechanisms J Clin Invest 1994 93371ndash379

18 Barnes PJ Beta Adrenergic Receptors and Their Regula-tion Am J Respir Crit Care Med 1995 152 838ndash860

19 Torphy TJ Phosphodiesterase Isoenzymes Am J RespirCrit Care Med 1998 157 351ndash370

20 Torphy TJ Beta-Adrenoceptors cAMP and AirwaySmooth Muscle Relaxation Challenges to the DogmaTrends Pharmacol Sci 1994 15 370ndash374

21 Spina D Rigby PJ Paterson JW Goldie RG Autora-diographic Localization of Beta-Adrenoceptors in Asth-matic Human Lung Am Rev Respir Dis 1989 1401410ndash1415

22 Martinsson A Larsson K Hjemdahl P Studies in Vivoand in Vitro of Terbutaline-Induced β-Adrenoceptor desen-sitization in Healthy Subjects Clin Sci 1987 72 47ndash54

23 Conolly ME Tashkin DP Hui KKP Littner MRWolfe RN Selective Subsensitization of Beta-AdrenergicReceptors in Central Airways of Asthmatics and NormalSubjects During Long-Term Therapy with Inhaled Salbu-tamol J Allergy Clin Immunol 1982 70 423ndash431

24 Hauk RW Bohm M Gengenback S Sunder-PlassmanL Fruhmann G Endmann E Beta-2 Adrenoceptors inHuman Lung and Peripheral Mononuclear Leukocytes ofUntreated and Terbutaline Treated Patients Chest 199098 376ndash381

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60 Anstead et al

KEY WORDS β2-Agonists β2-Adrenoceptors Asthma Plasma potassium

INTRODUCTION

β2-Agonist drugs are widely used in the treatment ofasthma as bronchodilator drugs they act by stimulation ofβ2-adrenoreceptors on airway smooth muscle The mostcommon standard route of administration is by inhalationHowever studies that have examined the direct effectsof these drugs on β2-adrenoreceptor function have usu-ally utilized either supratherapeutic inhaled doses or oralor parenteral doses (1ndash3) These drugs are also knownto have metabolic effectsmdashhypokalemia hyperglycemiaand hyperinsulinemiamdashthat are also mediated by β2-adrenoreceptor stimulation (45) Again most previousstudies of the metabolic effects have examined eithersupratherapeutic inhaled doses or parenteral or oral reg-imens (6ndash8) and the effects of standard therapeutic in-haled doses on the correlation between the bronchodilatorand metabolic effects of β2-agonists have not been syste-matically studied Furthermore there have been no studiesexamining the correlation between the metabolic effectsof β2-agonists and their effect on peripheral lymphocyteβ2-adrenoreceptor density

Therefore it is not known whether at therapeutic in-haled doses of β2-agonists bronchodilation occurs in asth-matics in the absence of metabolic effects and whetherthere are significant effects on peripheral lymphocyte β2-adrenoreceptor density We therefore designed this studyto examine the acute and chronic effects of standard dosesof an inhaled β2-agonist albuterol on bronchodilatationand peripheral blood lymphocyte β2-adrenergic receptordensity as well as on plasma potassium glucose and in-sulin in asthmatics and normal subjects

METHODS

A double-blind placebo-controlled crossover studywas performed in 11 nonsmoking subjects six normals(five males one female mean age = 283 plusmn 24 years)and five stable asthmatics (two males three females meanage = 230 plusmn 33 years) Written informed consent wasobtained from all subjects

All subjects had a complete medical history and exam-ination performed followed by spirometry at baseline andafter two puffs (90 microgpuff) of albuterol from a metereddose inhaler (MDI) Bronchodilator responsiveness wasdefined as an increase in FEV1 of at least 15 from base-line The asthmatic subjects were selected on the basis of

a history of asthma absence of any other systemic disor-der and documented responsiveness to inhaled albuterolNo subject had received inhaled or systemic steroids mastcell stabilizers or β2-agonists for at least 30 days beforeinitiation of the study The asthmatic subjects were al-lowed to use inhaled ipatroprium bromide for increasedasthma symptoms for the month before and during thestudy

The study was performed in two sequential treatmentperiods of 2 weeks each separated by a 2-week washoutperiod with each subject receiving inhaled albuterol threepuffs (90 microgpuff) four times a day from an MDI in oneof the 2-week treatment periods and inhaled placebo inthe other The sequence of drug vs placebo during thetwo treatment periods was based on a blind randomizedprotocol

Each subject attended the laboratory at the beginningand end of each 2-week period for a total of four vis-its After an overnight fast and having abstained fromcaffeine for a 12-hour period before each visit baselineblood samples were drawn at approximately the sametime of day (900 AM) on each occasion Blood sampleswere also drawn at 10 30 and 240 minutes after drug orplacebo administration Peripheral blood lymphocyte β2-adrenergic receptor density was measured on the baselineand 240-minute samples and plasma glucose potassiumand insulin were measured on all samples Spirometrywas performed by standard techniques (9) for measure-ment of FEV1 and FVC at baseline and at 10 30 and240 minutes

β2-Adrenergic receptor density on lymphocytes wasdetermined by Broddersquos technique (10) as described pre-viously (11) Lymphocytes were isolated from 40 mL ofblood by density gradient centrifugation with 12 mL ofFicoll-Paque and 25 mL of Hanks solution This was cen-trifuged at 400 G for 35 minutes at 4C The pellet was ag-itated with fresh Hanks solution to obtain a homogeneousmixture and an aliquot was counted on an automatedblood counter (Coulter S+IV Coulter Rcopy Instruments) Theisolation procedure took 3ndash4 hours and yielded a prepara-tion of 80ndash90 lymphocytes confirmed by microscopicidentification

Triplicate samples of 5 times 105 lymphocytes were in-cubated with eight concentrations of [125I]-(-) iodopin-dolol from 25 to 150 pM for 24 hours at 4C Nonspe-cific binding was determined using isoproterenol at a highconcentration (10 microM) to displace the receptor-boundligand The reaction was terminated by adding 10 mL of

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ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS


Table 1










Table 2










RESULTS


J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS

62 Anstead et al


DISCUSSION








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS







ACKNOWLEDGMENTS


REFERENCES








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS

64 Anstead et al



















J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

Order now








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS


Table 1










Table 2










RESULTS


J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS

62 Anstead et al


DISCUSSION








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS







ACKNOWLEDGMENTS


REFERENCES








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS

64 Anstead et al



















J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

Order now








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS

62 Anstead et al


DISCUSSION








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS







ACKNOWLEDGMENTS


REFERENCES








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS

64 Anstead et al



















J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

Order now








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS







ACKNOWLEDGMENTS


REFERENCES








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS

64 Anstead et al



















J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

Order now








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

ORDER REPRINTS

64 Anstead et al



















J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

Order now








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

Order now








J A

sthm

a D

ownl

oade

d fr

om in

form

ahea

lthca

rec

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 10

26

14Fo

r pe

rson

al u

se o

nly

Effects of Therapeutic Doses of Albuterol on β 2 -Adrenergic Receptor...

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Transcript of Effects of Therapeutic Doses of Albuterol on β 2 -Adrenergic Receptor...