Abstract
Given the previous evidence for involvement of prostanoid EP1 receptors in facilitation of the bladder afferent nerve activity and micturition reflex, the present study investigated the effect of ONO-8130, a selective EP1 receptor antagonist, on cystitis-related bladder pain in mice. Cystitis in mice was produced by intraperitoneal administration of cyclophosphamide at 300mg/kg. Bladder pain-like nociceptive behavior and referred hyperalgesia were assessed in conscious mice. Phosphorylation of extracellular signal-regulated kinase (ERK) in the L6 spinal cord was determined by immunohistochemistry in anesthetized mice. Cyclophosphamide treatment caused bladder pain-like nociceptive behavior and referred hyperalgesia accompanying cystitis symptoms, including increased bladder weight and vascular permeability and upregulation of cyclooxygenase-2 in the bladder tissue. Oral preadministration of ONO-8130 at 0.3-30 mg/kg strongly prevented both the bladder pain-like behavior and referred hyperalgesia in a dose-dependent manner, but had slight effect on the increased bladder weight and vascular permeability. Oral ONO-8130 at 30 mg/kg also reversed the established cystitis-related bladder pain. Intravesical administration of prostaglandin E2 caused prompt phosphorylation of ERK in the L6 spinal cord, an effect blocked by ONO-8130. Our findings strongly suggest that the prostaglandin E2/EP1 system participates in processing of cystitis-related bladder pain, and that EP1 antagonists including ONO-8130 are useful for treatment of bladder pain, particularly in interstitial cystitis. Prostaglandin E2 contributes to cystitis-related bladder pain via EP1 receptors in mice, indicating possible therapeutic usefulness of selective EP1 antagonists.