Bradykinin-Induced Responses in a Coaxial Bioassay System Composed of Rat Anococcygeus Muscle and Guinea Pig Trachea

Abstract

1. Epithelium-dependent effects of bradykinin (BK) were investigated in a coaxial bioassay system which consisted of guinea pig trachea as donor organ and rat anococcygeus muscle as test tissue. 2. BK (10 −9 to 10 −5 M) produced concentration-dependent relaxations on the phenylephrine (3×10 −6 M)-precontracted rat anococcygeus muscle mounted alone. Relaxations decreased significantly when muscle was mounted in epithelium-intact trachea. There was also a significant difference between the relaxations obtained in the muscle within epithelium-intact and epithelium-denuded trachea (at 10 −7 to 10 −5 M concentrations). 3. Capsaicin (10 −5 M) pretreatment did not change BK (10 −9 to 10 −5 M)-induced relaxations in each preparation compared with vehicle pretreatment. Indomethacin (10 −6 M) in combination with thiorphan (10 −5 M) and atropine (10 −6 M) did not affect the BK-induced relaxations of the muscle within capsaicin-pretreated epithelium-intact or denuded trachea. 4. CGS 8515 (a specific 5-lipoxygenase inhibitor, 10 −6 M) did not change BK (10 −5 M)-induced relaxation on the muscle alone, and caused an increase of BK-induced relaxation on the muscle within epithelium-intact trachea compared with that obtained without CGS 8515. 5. Results showed that epithelial or nonepithelial factors were capable of modulating the responsiveness of rat anococcygeus muscle to BK. The decreased relaxation by BK in anococcygeus muscle did not occur by the release of cyclooxygenase products or tachykinins from tracheal epithelium, but it may have occurred by the contractile action of lipoxygenase product secreted by nonepithelial sources. In addition, BK might stimulate the secretion of an epithelium-derived inhibitory factor from the trachea.