COMPARISON OF PARAMETERS OF IN-VITRO LYMPHOCYTE BETA-2-ADRENOCEPTOR FUNCTION IN NORMAL AND ASTHMATIC SUBJECTS

There is conflicting data in the literature as to whether subsensitivity of in-vivo beta2-adrenoceptor (beta2-AR) responses in patients with asthma is due to an endogenous defect of beta2-AR or an effect of exogenous beta2-agonist therapy. The purpose of the study was to compare in-vitro parameters of lymphocyte beta2-AR function in eight age and sex matched normal [FEV1, 98 (2) % predicted] volunteers and asthmatic [FEV1, 60 (5) % predicted] subjects. The asthmatic group were washed out for 4 weeks by substituting inhaled beta2-agonist therapy with ipratropium bromide, in order to exclude possible exogenous effects of beta2-agonist exposure. Receptor binding affinity (K(d)) and density (B(max)) were evaluated using (-)I-125-iodocyanopindolol and maximal cAMP response (E(max)) was assayed following stimulation with isoprenaline (10(-4)M). No significant differences were found between the normal and asthmatic group for K(d) (pmol.l-1): 9.65 vs 10.2, B(max) (fmol/10(6) cells): 1.9 vs 1.6, or E(max) (pmol/10(6) cells): 4.24 vs 4.85.Thus, parameters of beta2-AR function are unaltered in asthmatic patients who have not been exposed to beta2-agonists, suggesting that asthma is not associated with an endogenous defect of beta2-AR.