Abstract: Objective To investigate the neuronal nitric oxide synthase (nNOS) distribution in intramural striated sphincter of female rats. Methods 4 female Wistar rats were anesthetized with chloral hydrate. The whole bladder and urethra specimen were harvested, fixed in formalin and imbedded in paraffin wax. Longitudinal and transverse sections were developed with 2 urethra respectively. Routine HE staining and Mallory phosphotungstic acid-hematoxylin staining were used for observation of urethral microstructure. nNOS distribution in intramural striated sphincter was determined with immunohistochemical staining. Results The urethras of female Wistar rat were tubular structure about 1.5～2.0 cm long. From outside inward,the structure included circular striated muscle layer,circular smooth muscle layer,longitudinal smooth muscle layer,dense connective tissue and epithelium. The longitudinal sections showed intramural striated muscle predominates the middle and distal third,not the whole urethral length. The transverse sections showed intramural striated muscle is closed ring shape,about 5～10 layers uneven distributed with more layers in the posterior wall than in the front wall. Strong positive expression of nNOS immunoreactivity was found in some intramural striated muscle fiber. Conclusion nNOS expresses in some intramural striated muscle fiber, surggesting nitric oxide may play an important role on intramural striated sphincter.

Key words: intramural striated sphincter, nitric oxide synthase (NOS), urethra, rats