Beta-adrenoceptor responses to inhaled salbutamol in normal subjects

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Abstract
Summary The aim of the present study was to quantify and compare the airways and systemic beta-adrenoceptor responses to inhaled salbutamol in normal subjects. Seven non-atopic, normal subjects were given cumulative doubling doses of inhaled salbutamol (100 µg to 4000 µg) or placebo in a single-blind cross-over design. Airways (sGaw, FEF 50%, FEF 25%), tremor, haemodynamic and metabolic responses were measured at each dose increment. There were dose-related changes in sGaw, FEF 50% and FEF 25% up to a plateau at 1.0 mg. Analysis of individual responses showed that most subjects required either 1.0 or 2.0 mg for maximum bronchodilatation, independent of the parameter of airflow. There was no correlation between maximum response and baseline airway calibre. In contrast to airways effects, systemic beta-adrenoceptor responses did not occur until 500 µg, and a ceiling in the dose-response curve was not reached. Therer were significant correlations between air-ways, tremor and haemodynamic responses, and between different metabolic variables. The intraindividual variability was greatest for tremor and sGaw, although this was small in comparison to the size of maximum change with salbutamol. The converse applied to the hypomagnesaemic response.