Role of Nitric Oxide in Proximal Urethral Relaxation of the Rat

Jung, Hee Chang; Kim, Uk; Park, Tong Choon

Abstract

Recently, it is well established that nitric oxide synthase (NOS) produces nitric oxide (NO), which is known to act as an important neural mediator of smooth muscle relaxation in various organs. The present study was undertaken to investigate the role played by NO in relaxing bladder outlet by correlating its action with the existence, distribution and activity of NOS. The experiments consisted of nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining for the identification of NOS containing nerve fibers, NADPH diaphorase activity with spectrophotometric assay for NOS catalytic activity, Western blot analysis with polyclonal antibrain NOS antibody for the expression of neuronal NOS, and in vivo isovolumetric bladder contraction (IBC) and reflex urethral .relaxation (RUR) for the physiologic role of NO. On NADPH diaphorase histochemistry in the rat, NADPH positive staining was localized in neurons innervating the lower genitourinary tract including the urinary bladder and the proximal urethra. NADPH positive nerve fibers were mainly found in urethral area, whereas they were less common in detrusor. In assay of NADPH diaphorase activity on various organs of the rat, the NOS activity regionally predominated in the cerebellum, proximal urethra, and urinary bladder in the order of frequency, which were correlated with the RESULTS of Western blot. Subsequent investigations were focused on the physiologic role of NO in the reflex changes in bladder outlet activity during micturition in the rat. During IBC, the urethra exhibited reflex responses characterized by a decrease in RUR in conjunction with a rise in IBC. Administration of NOS inhibitor, Nw-nitro-L-arginine, reversibly decreased the magnitude and duration of RUR, and this effect was reversed by administration of L-arginine. From these RESULTS, it is suggested that the neuronal form of constitutive NOS in the bladder outlet synthesizes NO by its catalytic action, which mediates relaxation of bladder outlet during micturition.