Contribution of Prostaglandin E₂ to Bradykinin-Induced Contraction in Rabbit Urinary Detrusor

Abstract

Bradykinin (100 pM to 1 μM) contracted the rabbit urinary detrusor in vitro. The sensitivity to bradykinin was about 1000 times higher than that to acetylcholine (ACh) on a molar basis. The contractile response to bradykinin was unaffected by atropine, diphenhydramine, FPL-55712, methysergide, prazosin or tetrodotoxin, indicating that the contraction was not mediated via the release of ACh, histamine, peptide leukotrienes, serotonin or catecholamine. The bradykinininduced contraction was, however, inhibited by indomethacin (5 μM), a cyclooxygenase inhibitor. Caffeic acid (10 μM), a lipoxygenase inhibitor, did not affect the contraction. Bradykinin (1 nM to 100 nM) stimulated the release of prostaglandin E₂ from the detrusor in a concentration-dependent manner, and the release was abolished by treatment with indomethacin (5 μM). Prostaglandin (PG) E₂ contracted the urinary detrusor with an EC50 of about 0.1 μM. Adenosine 5'-triphosphate (ATP), a stimulator of PG synthesis, also contracted the muscle with an EC50 of about 100 μM. [¹⁴C]Arachidonic acid was converted to PGE₂ and F_2α when it was incubated with the 700×g supernatant of the muscle homogenate. However, neither bradykinin nor ATP stimulated the PG synthesis in the supernatant. These results showed that bradykinin and ATP did not affect the cyclooxygenase and/or PG degradation system. On the other hand, when the intact detrusor muscle was incubated with [¹⁴C]arachidonic acid, bradykinin and ATP stimulated the PG synthesis, and the stimulated synthesis was inhibited by indomethacin. Mepacrine, a phospholipase A₂ inhibitor, more potently inhibited the bradykinin and ATP-induced contractions than the ACh-induced one. Therefore, bradykinin as well as ATP would stimulate phospholipase, probably the A₂-type, after binding of its receptor, and contract rabbit urinary detrusor mediated via PGE₂ converted from arachidonic acid.