EFFECTS OF BETA(2)-ADRENOCEPTOR AGONISTS ON ANTI-IGE-INDUCED CONTRACTION AND SMOOTH-MUSCLE REACTIVITY IN HUMAN AIRWAYS

1 The beta(2)-adrenoceptor agonists, salbutamol, salmeterol and RP 588 02 relaxed basal tone of human isolated bronchial smooth muscle. Salme terol- and RP 58802-induced relaxations persisted for more than 4 h wh en the medium was constantly renewed after treatment. 2 Salbutamol, sa lmeterol and RP 58802 reversed histamine-induced contractions in human airways (pD(2) values: 6.15 +/- 0.21, 6.00 +/- 0.19 and 6.56 +/- 0.12 , respectively). 3 Anti-IgE-induced contractions were significantly in hibited immediately after pretreatment of preparations with beta(2)-ad renoceptor agonists (10 mu M). However, when tissues were treated with beta(2)-agonists and then washed for a period of 4 h, salmeterol was the only agonist which significantly inhibited the anti-IgE response. 4 Histamine response curves were shifted to the right immediately afte r pretreatment of tissues with the beta(2)-adrenoceptor agonists (10 m u M; 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 l eukotriene C-4 (LTC(4)) were not significantly modified after beta(2)- agonist pretreatment 5 These results suggest that beta(2)-adrenoceptor agonists may prevent anti-IgE-induced contraction by inhibition of me diator release rather than alterations of those mechanisms involved in airway smooth muscle contraction.