| Abstract: | The effects of theophylline (THEO), terbutaline (TER), and ipratropium bromide (IPRA), given i.v. alone or in combination, were studied on leukotriene D4 (LTD4)-induced airway obstruction in anaesthetized guinea pigs. LTD4 (0.1-1.6 microgram/kg i.v.) obstructed small airways more than large ones as assessed in terms of relative changes of lung resistance (RL) and dynamic lung compliance (CDyn). A slight tachyphylaxis to LTD4 was observed after repeated administration, especially in the responses of large bronchi. The airway effects of LTD4 were almost totally abolished by prior administration of indomethacin (5 mg/kg i.v.) suggesting a central role of secondarily released cyclo-oxygenase products in this model. THEO (1 to 20 mg/kg) and TER (10 to 400 micrograms/kg) antagonized dose-dependently the LTD4 (0.4 microgram/kg i.v.) induced rise in RL and decrease in CDyn, whereas IPRA (10 to 400 micrograms/kg) failed to show comparably activity. THEO 5 and 20 mg/kg proved highly efficient also on the dose-related airway challenge by LTD4 (0.6 and 1.5 microgram/kg i.v.). Combined treatment with THEO 5 mg/kg + Ter 80 micrograms/kg resulted in an additive effect on RL and CDyn. The combination to THEO 20 mg/kg + TER 80 micrograms/kg was about as effective as THEO 20 mg/kg alone suggesting a nearly maximal effect by the latter treatment. It is concluded that THEO is considerably more efficient on the LTD4-induced airway obstruction than previously observed on the cholinergic model in guinea pigs. Combined treatment with THEO and beta 2-adrenoceptor agonist may antagonize in an additive manner the LTD4 effects on large and small airways. |
