Response of rabbit detrusor muscle to bradykinin

The contractile response to bradykinin was studied in isolated longitudinal strips of detrusor muscle from rabbit urinary bladder. Strips responded slowly with contractions which were comparable in magnitude to acetylcholine but much greater than those produced by arachidonic acid. The bradykinin dose-response curve was very shallow (Clark's ratio = 10^-5), with an ED50 of 0.2 μM. Bradykinin-induced contractions were unaffected by 0.4 μM atropine or 0.2 μM eserine. This suggests, in contrast to reports on rat bladder, that acetylcholine release does not contribute to the response. However, pretreatment with 10 μM naproxen antagonized bradykinin-induced contractions without affecting acetylcholine. It is concluded that, as in many other tissues, in the urinary bladder at least part of the response to bradykinin is mediated through prostaglandins. Bradykinin probably also has a direct action since higher concentrations are less susceptible to naproxen, and it produces a much greater contraction than the maximum achievable with arachidonic acid.