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European Journal of Pharmacology 318 1996 123–129
Effect of short- and long-acting b -adrenoceptor agonists on pulmonary
2
b -adrenoceptor expression in human lung
2
Masanori Nishikawa
1
, Judith C.W. Mak, Peter J. Barnes
)
Department of Thoracic Medicine, National Heart and Lung Institute, Imperial College of Science, Technology and Medicine,
DoÕehouse Street, London SW3 6LY, UK
Received 18 July 1996; revised 2 September 1996; accepted 20 September 1996
Abstract
b-Adrenoceptor agonists induce the down-regulation of b -adrenoceptors and mRNA expression in animal lung. The down-regulation
2
of b -adrenoceptors may limit the therapeutic efficacy of b -adrenoceptor-mediated bronchodilators in obstructive airways disease. We
22
examined the effects of three selective b -adrenoceptor agonists, salbutamol, salmeterol and formoterol on b -adrenoceptor binding and
2 2
mRNA levels in human lung in vitro. Human lung was obtained from cardiac transplantation donors. Peripheral lung was chopped and
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incubated with three selective b -adrenoceptor agonist for 3 h or 24 h at three different concentrations 0.1, 1 and 10 mM . The affinity
2
w
125
x
and density of b -adrenoceptors was determined by I iodocyanopindolol equilibrium binding in a lung membrane preparation in the
2
ŽÄwŽ.x 4 w Ž
presence of 0.1 mM CGP 20712 A 1- 2- 3-carbamoyl-4-hydroxy phenoxy ethylamino -3- 4- 1-methyl-4-trifluoromethyl-2-
. x .
imidazolyl phenoxy -propan-2-ol , a selective b -adrenoceptor antagonist. Although treatment with salbutamol for 3 h did not change
1
b -adrenoceptor density, both salmeterol and formoterol reduced b -adrenoceptor density, and exposure to each agonist for 24 h reduced
2 2
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b -adrenoceptor density at all concentrations. Treatment with 10 mM salmeterol increased the eqilibrium dissociation constant K , and
2 d
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also shifted the competition curves of y -isoprenaline to the left. b -Adrenoceptor mRNA, measured by Northern blot analysis using a
2
human b -adrenoceptor cDNA probe, was reduced after exposure to all b -adrenoceptor agonists at 3 h. Our data provide evidence for
2 2
down-regulation of b -adrenoceptor protein and mRNA after selective b -adrenoceptor agonist treatment in human lung.
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Keywords: Down-regulation; b -Adrenoceptor; Salbutamol; Salmeterol; Formoterol; Lung, human
2
1. Introduction
Selective b -adrenoceptor agonists are far the most
2
effective bronchodilators in current use for the treatment of
asthma. When taken by inhalation they rapidly relieve
symptoms and protect against all known bronchoconstric-
tor mechanisms, since they are functional antagonists and
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are effective on large and small airways Nelson, 1995 . It
is common clinical practice for b -adrenoceptor agonists
2
to be given as a regular medication, but this may mask the
underlying inflammatory process and the need for anti-in-
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flammatory drugs Barnes and Chung, 1992; Barnes, 1995 .
)
Ž. Ž.
Corresponding author. Tel.: 44-171 351-8174; Fax: 44-171 351-
5675.
1
Present address: The First Department of Internal Medicine, Yoko-
hama City University, School of Medicine, 3–9 Fuku-ura, Kanazawa-ku,
Yokohama, 236, Japan.
There is some evidence that regular treatment with b -
2
adrenoceptor agonists makes asthma more difficult to con-
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trol Sears et al., 1990; Taylor et al., 1993 and may even
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increase airway inflammation Manolitsas et al., 1995 .
Whether desensitization or tolerance to inhaled b -
2
adrenoceptor agonists is a clinical problem is still not
clear. Although there is no loss of bronchodilator response
to selective b -adrenoceptor agonists after regular treat-
2
Ž.
ment Tattersfield, 1985; O’Connor et al., 1992 , several
studies demonstrated loss of protection against bron-
choconstrictor challenges with both short-acting b -adren-
2
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oceptor agonists O’Connor et al., 1992; Cockcroft et al.,
.
1993 , and the long-acting b -adrenoceptor agonists, sal-
2
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meterol and formoterol Cheung et al., 1992; Yates et al.,
.
1995 . Down-regulation after selective b -adrenoceptor ag-
2
onist use could limit the therapeutic efficacy of b -adren-
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oceptor-mediated bronchodilation therapy in bronchial
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asthma Barnes and Chung, 1992 . Prolonged administra-
tion of b -adrenoceptor agonists induces the down-regu-
2
0014-2999r96r$15.00 Copyright q 1996 Elsevier Science B.V. All rights reserved.
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PII S0014-2999 96 00769-8