ROLE OF NITRIC OXIDE (NO) IN FUNCTION OF LOWER URINARY TRACT

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[Aimes of study] We have investigated the physiological role of nitric oxide (NO) in isolated rabbit urethral strips or urethral smooth muscle cells. We also investigated the effects of PTIO on vesico-urethral function in the chronic spinal rabbits. In this project, we used a new class of NO scavengers, i.e., a series of derivatives of 2-phenyl-4, 4, 5, 5, -tetramethylimidazoline-oxyl 3-oxide (PTIO), which showed a radical-radical reaction with NO.[Methods] 1) Functional experiments : Urethra was isolated from adult female rabbits. The muscle strip was transferred to organ bath filled with Krebs-Henseleit solution, and end of each strip was connected to force displacement transduser, and isometric force was recorded. The muscle strip was contracted with 1 muM phenylephrine, and electrical field stimulation (EFS) was applied For measurement of N0^-_/N0^-_ (NOx) release from muscle strips, a microdialysis probe was inserted into the urethral strip, and was perfused with Krebs-Henseleit s … More olution. The dialyzate fraction obtained during BPS was infused into an automated NOx analyzing system based on the Griess reaction. 2) Experiments in caltured urethral smooth muscle cells : After removal of urethral epithelium, the urethral smooth muscle was cut into small pieces, and isolated by PBS with collagenase. The cell was transffered to MEM culture solution and incubated CO2 incubator. The establised cultured urethral smooth muscle cell was transffered to small bath with electrode of EFS, and the change in the length of the cell was evaluated by videomicrometer using microscope. 3) Experiments in spinal rabbits : Laminectomy was performed and spinal cord was transected at thracic level T8-T9 in adult femal rabbits. Eight weeks after operation, double lumen catheter was placed into bladder, and urodynamic studies were performed. The effects of PTLO or L-NNA (NOS inhibitor) on each parameter was evaluated.[Results] EFS caused frequency-dependent relaxation responses in isoleted rabbit urethral strips. Pretreatment with L-NNA almost completely inhibited the relaxation responses, and PTIO inhibited the relaxation by 45 %. During FES, NOx increased in the urethral strip and cultured cell. The increased NOx was inhibited by both L-NNA and PTIO.The inhibition was significantly larger in L-NNA than in PTIO.In the chronic spinal rabbits, the maximun bladder capacity was decreased and the maximum voiding pressure and the number of micturition reflax was significantly increased. The urethral closing pressure was significantly decresed. The intravenous injection on PTIO or L-NNA did not change the bladder function, but caused a significant incraese in the urethral closing pressure.[Conclusion] The data suggest that relaxation response in urethra was caused by both radical NO and NO bioaducts, and that PTIO was useful drug for urunary incontinece in the neurogenic condition. Less