Intratesticular Bradykinin Involvement in Rat Testicular Pain Models.

To clarify the role of bradykinin in urogenital pain, we investigated bradykinin involvement in rat models of testicular pain. Bradykinin (0.1, 0.3, 1, 3 and 10 mmol/L) or distilled water was injected into the testes of male Wistar rats, and induced pain behaviors in conscious rats were evaluated. The effect of pretreatment with bradykinin B2 receptor antagonist FK3657 on bradykinin-induced pain behavior was then examined. We also evaluated the analgesic effect of FK3657 in a rat acetic acid-induced testicular pain as well as changes in the intratesticular bradykinin concentration after testicular injection of acetic acid. An injection of bradykinin into the testes of conscious rats induced pain behaviors that were dose-proportionally reduced by prior administration of FK3657. In addition, FK3657 dose-dependently inhibited the pain responses induced by testicular injection of 1% acetic acid. An increase in intratesticular bradykinin concentration was detected after the testicular injection of 1% acetic acid. Here, we found that intratesticular bradykinin evokes pain behavior via stimulation of bradykinin B2 receptors and that intratesticular acetic acid injection induces intratesticular bradykinin synthesis, consequently leading to pain behavior. These findings suggest that the potential utility of bradykinin B2 receptor antagonists as a novel target for treating urogenital pain.