Effects of β2‐adrenoceptor agonists on anti‐IgE‐induced contraction and smooth muscle reactivity in human airways

Abstract

The β2‐adrenoceptor agonists, salbutamol, salmeterol and RP 58802 relaxed basal tone of human isolated bronchial smooth muscle. Salmeterol‐ and RP 58802‐induced relaxations persisted for more than 4h when the medium was constantly renewed after treatment. Salbutamol, salmeterol and RP 58802 reversed histamine‐induced contractions in human airways (pD2 values: 6.15 ± 0.21, 6.00 ± 0.19 and 6.56 ± 0.12, respectively). Anti‐IgE‐induced contractions were significantly inhibited immediately after pretreatment of preparations with β2‐adrenoceptor agonists (10 μm). However, when tissues were treated with β2‐agonists and then washed for a period of 4 h, salmeterol was the only agonist which significantly inhibited the anti‐IgE response. Histamine response curves were shifted to the right immediately after pretreatment of tissues with the β2‐adrenoceptor agonists (10 μm; 20 min), but maximal contractions were not affected. After a 4 h washing period, the histamine curves were not significantly different from controls. Concentration‐effect curves to acetylcholine (ACh) or leukotriene C4 (LTC4) were not significantly modified after β2‐agonist pretreatment. These results suggest that β2‐adrenoceptor agonists may prevent anti‐IgE‐induced contraction by inhibition of mediator release rather than alterations of those mechanisms involved in airway smooth muscle contraction. 1995 British Pharmacological Society