Selective subsensitization of beta-adrenergic receptors in central airways of asthmatics and normal subjects during long-term therapy with inhaled salbutamol |
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Authors: | Matthew E Conolly MD MRCP Donald P Tashkin MD Ka Kit Paul Hui MD Michael R Littner MD Robert N Wolfe MD |
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Institution: | 1. From the Divisions of Clinical Pharmacology and Pulmonary Disease, Departments of Medicine and Pharmacology, Center for the Health Sciences, UCLA School of Medicine, Los Angeles, Calif., USA;2. From the Divisions of Clinical Pharmacology and Pulmonary Disease, Departments of Medicine and Pharmacology, Sepulveda V.A. Medical Center, Los Angeles, Calif., USA |
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Abstract: | In five subjects with mild asthma and in five normal subjects, we determined the effect of a 4 wk course of inhaled salbutamol (albuterol), 200 μg q.i.d., on (I) acute bronchodilator responsiveness, (2) bronchial sensitivity to inhaled histamine, (3) beta-adrenergic protection against histamine-induced bronchospasm, and (4) beta-receptor density of peripheral blood lymphocytes. We observed a diminution in central airway bronchodilator responsiveness (as measured by airway conductance responses) to acutely inhaled salbutamol and to subcutaneous terbutaline in both groups of subjects, although only the response to subcutaneous terbutaline was statistically significant (p < 0.02). On the other hand, no impairment of small airway bronchodilator responsiveness was noted in either group of subjects when responses were measured as partial expiratory flow rates at 60% below total lung capacity. These findings suggest the development of selective subsensitization of beta-receptors in the larger central airways, where a proportionately greater amount of the inhaled beta-agonist aerosol would necessarily be deposited. A greater loss of protection against histamine-induced bronchospasm was seen in asthmatics than in normals (approximately twofold), although the difference was not significant. A modest but not significant reduction in peripheral blood lymphocyte beta-receptor density was observed by the end of the 4 wk treatment period. The possibility that the observed changes in bronchodilator responsiveness might influence the morbidity and mortality associated with bronchial asthma is discussed. |
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Keywords: | Forced expiratory volume in one second Specific airway conductance Maximum expiratory flow rate at 60% below total lung capacity calculated from the partial flow-volume curve Reprint requests to: Matthew E Conolly M D Department of Medicine UCLA School of Medicine Los Angeles CA 90024 |
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