| Abstract: | Pulmonary responses to intravenous leukotrienes C4, D4 and E4 administered as a bolus injection and by continuous infusion were studied in anesthetized guinea pigs. LTD4, LTC4 and LTE4 (respective ED50 of 0.21 ± .1, 0.64 ± .2 and 2.0 ± .1 μg kg−1) produced dose-dependent increases in insufflation pressure when given as a bolus injection to anesthetized guinea pigs (Konzett-Rössler). Bronchoconstriction was antagonized by FPL-55712 (50–200 μg kg−1), and indomethacin (50–200 μg kg−1) but was not significantly altered by mepyramine (1.0 mg kg−1), methysergide (0.1 mg kg−1), intal (10 mg kg−1) mepacrine (5 mg kg−1) or dexamethasone (10 mg kg−1). The beta adrenoceptor blocker, timolol (5 μg kg−1) produced a significantly greater potentiation of the responses to the leukotrienes than to arachidonic acid, histamine and acetylcholine. Responses to bolus injection of LTE4 but not LTD4 or LTC4 were partially antagonized by atropine (100 μg kg−1) and bilateral vagotomy. In experiments of a different design, continuous infusion of LTD4 and LTE4 (2.8–3.2 μg kg−1 min−1) into indomethacin-treated animals produced slowly developing increases in pulmonary resistance and decreases in compliance. The increase in resistance produced by LTE4 and LTD4 was partly reversed by intravenous FPL-55712 (1.0 mg kg−1) and atropine (100 μg kg−1) but was almost completely reversed by FPL-55712 (3 – 10 mg kg−1). These findings indicate that leukotrienes can produce bronchoconstriction in guinea pigs through cyclooxygenase-dependent and cyclooxygenase independent mechanisms both of which are blocked by FPL-55712. Cholinergic mechanisms are involved in the mediation of part of the response to bolus injection of LTE4 as well as a small part of the initial response to continuous infusion of LTD4 and LTE4. Intrinsic beta adrenoceptor activation serves to down modulate responses to the leukotrienes to a greater extent than responses to arachidonic acid, histamine and acetylcholine. |
