Terbutaline acts at multiple sites to inhibit bronchoconstriction induced by dry air in canine peripheral airways

We examined the effect of the beta 2-agonist terbutaline on dry airflow-induced bronchoconstriction (AIB) in the canine lung periphery. Using a wedged bronchoscope technique, collateral resistance (Rcs) and airway wall temperature (Taw) were measured before and after a 2-min exposure to dry air. When sublobar segments were challenged with dry air, Taw fell during challenge (p less than 0.001), and Rcs increased 5 min postchallenge (p less than 0.01). Pretreatment with terbutaline (100 micrograms/kg) reduced the fall induced by dry-air challenge in Taw by 37% and the subsequent rise in Rcs by 87%. Terbutaline significantly reduced the concentrations of thromboxane B2 (TxB2) and prostaglandin D2 (PGD2), and decreased the concentration of epithelial cells recovered in bronchoalveolar lavage fluid 5 min postchallenge. In addition, terbutaline attenuated histamine- and PGD2-induced constriction. Finally, peripheral lung sensitivity (as assessed by delta Rcs/delta Taw) to challenge after treatment with terbutaline was significantly less than that calculated for untreated control animals (p less than 0.05). These data are consistent with the idea that terbutaline attenuates AIB by (1) facilitating replacement of water lost during exposure to dry air, (2) inhibiting mediator production and release from osmosensitive cells, and (3) reducing smooth muscle responsiveness.