The external urethral sphincteric mechanism generates forces which seal the urethra and can be measured as urethral pressure. Resting pressure can be augmented transiently through a reflex pathway during increases in intra-abdominal pressure. The exact role of the various components of the urethral wall that generate this pressure is so far unknown. Urethral contributions to continence come from the mucosal hermetic seal, the submucosa and its vascular filling and the smooth and striated muscle. In humans α1-adrenoceptor antagonists can reduce urethral pressure, whereas agonists have little effect. A significant part of urethral resting tone is thought to be mediated through the smooth muscles. In vitro, longitudinal and circular smooth muscle components possess spontaneous tone and are innervated by excitatory and inhibitory nerves. Both types possess α1-adrenoceptors and contract on stimulation of intrinsic sympathetic nerves or application of α1-adrenoceptor agonists. In human urethra, longitudinal smooth muscle predominates but its functional role is unclear. α1 stimulation may also affect the vasculature of the submucosa, the striated muscle of the urethra or transmitter release from neurones in the control pathways. Insufficient knowledge of α1-adrenoceptor distribution and function within the urethra and the surrounding tissues currently prevents accurate prediction of the therapeutic potential of α1-adrenoceptor ligands.

Keywords:
Noradrenaline, Urethra, Alpha-adrenoceptors, Smooth muscle
1.
Thind P: The significance of smooth and striated muscles in sphincter function of the urethra in healthy women. Neurourol Urodyn 1995;14:585–618.
2.
Greenland JE, Dass N, Brading AF: Intrinsic urethral closure mechanisms in the female pig. Scand J Urol Nephrol 1996;30S:179:75–80.
3.
Greenland JE, Brading AF: The in vivo and in vitro effects of hypoxia on pig urethral smooth muscle. Br J Urol 1997;79:525–531.
4.
Macneil HF, Turner WH, Brading AF: The physiology of the pig urinary sphincter. Neurourol Urodyn 1991;10:351–352.
5.
Dixon J, Gosling J: Structure and innervation in the human. In: Torrens M, Morrison JFB, ed. The physiology of the lower urinary tract. Berlin: Springer-Verlag, 1987:3–22.
6.
Bridgewater M, Davies JR, Brading AF: Regional variations in the neural control of the female pig urethra. Br J Urol 1995;76:730–740.
7.
Dass N: Studies of the anatomy and autonomic innervation of the vesicourethral junction and urethra. D. Phil., Oxford University, UK 1997.
8.
Fowler CJ, Fowler C: Clinical neurophysiology. In: Torrens M, Morrison JFB, ed. The physiology of the lower urinary tract. Berlin, Springer, 1987:309–332.
9.
Elbadawi A, Schenk EA: A new theory of the innervation of bladder musculature. 4. Innervation of the vesicourethral junction and external urethral sphincter. J Urol 1974;111:613–615.
10.
Kuba K, Tomita T: Noradrenaline action on nerve terminal in the rat diaphragme. J Physiol (Lond) 1971;217:19–31.
11.
Bridgewater M, Macneil HF, Brading AF: Regulation of tone in pig urethral smooth muscle. J Urol 1993;150: 223–228.
1999
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