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Aim:Recent studies have shown that various factors contribute to the increased excitability into the bladder afferent nerves in spinal cord injury (SCI) rats. It has been reported that prostaglandins (PG) act as local modulators of reflex micturition in pathological conditions. In the present study, we measured the amount of PGE 2 release from the bladder of chronic SCI rats. Methods: Spinal cord was transected at the level of T8-9 in adult female Sprague-Dawley rats. After 10 weeks, specimens of the urinary bladder were obtained from SCI rats and sham-injured control rats, and bladder strips were dissected from the bladder. Using an muscle-bath technique and a microdialysis procedure, the dialysate, containing substance released from bladder strips, was collected. Then the amount of PGE 2 in the dialysate was measured by radioimmunoassay. Results: Excretion of urinary PGE 2 was significantly higher in SCI rats than in control rats. PGE 2 release from bladder strips was significantly higher in SCI rats than in control rats. Removal of urothelium caused significant decreases in PGE 2 release in both control and SCI rats. Stretches of the bladder strips caused significant resting tension-dependent increases in PGE 2 release from the strips with urothelium. Conclusions: The present data suggest that bladder urothelium partly contributes to the increase in PGE 2 release from the bladder, and that bladder distension may cause increases in PGE 2 release in SCI rats.

KRP-197, 4-(2-methylimidazol-l-yl)-2,2-diphenylbutyramide, is a newly synthesized antimuscarinic drug, developed for the treatment for overactive bladder. For evaluation of pharmacological characteristics of KRP-197, we investigated whether it influenced both prejunctional and postjunctional muscarinic receptors on the isolated human detrusor smooth muscles as compared with the effects of atropine, oxybutynin, and propiverine. Using the muscle bath technique, we investigated the effects of various antimuscarinic drugs on the contractions induced by carbachol, KCl, CaCl₂, and electrical field stimulation. Furthermore, using high-performance liquid chromatography with a microdialysis technique, we measured the acetylcholine release from the muscle strips during electrical field stimulation. The effects of various antimuscarinic drugs on acetylcholine releases were also evaluated. Pretreatment with various antimuscarinic drugs caused parallel shifts to the right in carbachol-induced concentration-response curves. The rank order of pA₂ values was KRP-197 ≧ atropine > oxybutynin > propiverine. Atropine and KRP-197 did not cause significant inhibition of KCl- and CaCl₂-induced contractions. All drugs caused concentration-dependent inhibitions in electrical field stimulation-induced contractions. Pretreatment with atropine and propiverine did not cause significant changes in electrical field stimulation-induced acetylcholine release. However, KRP-197, and oxybutynin caused significant decreases in acetylcholine release. The present study demonstrates that KRP-197 has an inhibitory effect on postjunctional muscarinic receptors as well as on prejunctional muscarinic receptors to modulate acetylcholine release in human detrusor smooth muscles. The findings suggest the usefulness of KRP-197 as a therapeutic drug for an overactive bladder with symptoms of frequency, urgency, and urge incontinence.

Introduction: To investigate the mechanism of voiding dysfunction in non-insulin-dependent diabetes mellitus, we attempted to measure the acetylcholine (ACh) release using an in vivo microdialysis technique and measuring the detrusor pressure after electrical field stimulation (EFS) of the pelvic nerve. Materials and Methods: Eight- and 32-week-old female Goto-Kakizaki (GK) rats (non-insulin-dependent diabetes mellitus model) and age-matched female Wistar rats (controls) were used in this study. The pelvic nerve was exposed on a bipolar platinum electrode to EFS, and a cannula was inserted into the bladder to measure the detrusor pressure. The microdialysis probe was inserted into the bladder wall and was connected to a microinfusion syringe pump. Dialysate was constantly perfused, collected in a microtube, and then injected into the ACh assay system. Histological examinations were performed by staining with hematoxylin and eosin and S-100 immunohistochemical staining in bladder preparations of both GK and control rats. Results: In 8-week-old rats, both detrusor pressures and amounts of ACh release of GK rats were not significantly different from those of control rats. In 32-week-old rats, both detrusor pressures and ACh releases were only significantly increased at 5 and 10 Hz of EFS. In the histological study, the number of nerve fibers or bundles of 32-week-old GK rats was significantly decreased as compared with control rats. Conclusion: The present data suggest that the decrease in EFS-induced ACh release in GK rats, which may be caused by the decreased number of nerve fibers, may contribute to the decrease in bladder contractions.

Background: The effects of castration on nitric oxide- mediated relaxations and nitric oxide synthase activity in male rat corpus cavernosum smooth muscles. Methods: Eight-week-old male rats were assigned to two groups: control (sham operated) and castrated animals. After 8 weeks, corpus cavernosum smooth muscle strips were mounted in an organ bath for isometric tension recordings. Electrical field stimulation (EFS) was applied to the strips precontracted with 30 µM phenylephrine. The microdialysis probe was inserted into the strip, and Krebs-Henseleit solution was perfused into the probe. The dialysate during EFS and cholinergic stimulation was collected, and the amount of NO^–₂/NO^–₃ (NOx) released in the dialysate was measured by the Greiss method. Sodium nitroprusside and carbachol were cumulatively added to the strips precontracted with 30 µM phenylephrine. Results: EFS caused frequency-dependent relaxations and NOx releases in the strips. Pretreatment with N^ω-nitro-L-arginine (100 µM) and tetrodotoxin (1 µM) completely inhibited relaxations and NOx releases. The maximum relaxation in the castration group was significantly greater than that in the control group. The release of NOx was significantly greater in the castration group than in the control group. Sodium nitroprusside relaxed the tissues in both groups similarly. Carbachol failed either to relax the tissue or to increase the amount of NOx production in the tissue. Conclusion: The present data suggest that castration enhances nitric oxide synthase activity and nitric oxide-mediated relaxations in the male rat corpus cavernosum.