Effects of bradykinin and leukotrienes B4 and D4 on the bovine bronchial artery in vitro: role of the endothelium.

The effects of bradykinin, leukotriene (LT) B4 and LTD4 on the bovine bronchial artery were studied using isolated, perfused vessel segments. Intrapulmonary bronchial arteries were precontracted to the EC50 of 5-hydroxytryptamine in the organ bath, after which increasing concentrations of bradykinin, LTB4 or LTD4 were perfused through the vessel lumen. In arteries with intact endothelium, bradykinin induced a concentration-dependent relaxation beginning at 1 pmol/l (p less than 0.01), whereas LTD4 and LTB4 had no significant effect. Indomethacin (10 mumol/l) significantly (p less than 0.01) inhibited bradykinin-induced relaxation with an increase in the IC50 from 0.11 +/- 0.08 nmol/l to 0.51 +/- 0.10 nmol/l (p less than 0.05). In endothelium-denuded arteries bradykinin had no observed effect, whereas LTB4 and LTD4 significantly increased tone with threshold concentrations of 50 pmol/l (p less than 0.025) and 5 pmol/l (p less than 0.05), respectively. The data indicate that in the bronchial artery: 1) bradykinin is a potent vasodilator; 2) bradykinin-induced relaxation is endothelium-dependent and only partially blocked by a cyclooxygenase inhibitor; 3) removal of the endothelium unmasks a potent contractile effect of LTB4 and LTD4.