The machanisms that mediate the actions of bradykinin on ureteral motility are poorly defined and mediation via prostaglandins has not been examined. Therefore, the effects of bradykinin on contractility and the possible mediator role of prostaglandins have been investigated in sheep ureter. At the concentrations of 10-8, 10-7 and 10-6M, bradykinin elicited marked reductions in contractile force. When ureteral strips were treated separately with 10-6M indomethacín, 2x10-6M sodium salicylate and 10-5 M aspirin, each drug produced a significant decrease in contractile force. In strips in which prostaglandin synthesis was inhibited by the above concentrations of indomethacin, sodium salicylate and aspirin, 10-7M bradykinin significantly decreased the contractility. From these data, we concluded that in ureter bradykinin decreases contractility via a mechanism not involving prostaglandin generation