The urethral striated sphincter in adult male rat
- 230 Downloads
This study reports the morphology of the urethral sphincter in adult male rats, mainly the histological aspects, the features of the endplates, and the heavy myosin chain distribution in the striated fibres. First, the prostate is entirely out of the striated sphincter, which is surprising when compared to man. Second, the urethral striated sphincter consists of two lateral fascicles separated by an anterior and a posterior strip of connective tissue, which extend from the prostatic urethra (i.e. the part of the urethra which runs though the prostate) to the bulb of the penis. An additional third fascicle of striated muscle (SM) covers the caudal part of the anterior connective strip of the membranous urethra (i.e. the urethra which extends from its prostatic part to the bulb of the penis). In the membranous urethra, the striated sphincter surrounds directly the urethral lumen without intercalated smooth muscle. In urethral cross sections, the endplates detected by α-bungarotoxin, which binds to nicotinic receptors, are clustered in the postero-lateral part of the lateral fascicles. The cross-sectional area of the urethral striated fibres shows a bimodal distribution: the largest fibres are located at the periphery of the sphincter and these fibres express only fast myosin heavy chains (MHC) as shown by immunochemistry. The smallest fibres are less numerous and are situated near the lumen co-expressing fast and slow MHC. All the striated fibres express desmin and dystrophin as SM fibres do. Taken together, these results suggest that the urethral striated fibres in male rat present the same characteristics as those of the skeletal muscles. The predominance of fast fibres is consistent with phasic contractions playing a role not only during micturition and urinary continence but also probably during ejaculation.
KeywordsProstatic urethra Membranous urethra Fibre type Myosin heavy chain Continence Micturition Histology
We thank Daniel Stockholm for his friendly help in confocal microscopy.
- Dorschner W, Stolzenburg JU, Leutert G, Dieterich F, Rassler J (1994) A new theory of micturition and urinary continence based on histomorphological studies. Part I-V: Urol Int 52:61–64, 154–158, 185–188, 189–193, 53:34–37Google Scholar
- Dubovitz V (1985) Muscle biopsy: a practical approach. Eds. Baillière Tindall, 2nd edn. London, p 14Google Scholar
- Junemann KP, Lue TF, Schmidt RA, Tanagho EA (1988) Clinical signifiance of sacral and pudental nerve anatomy. J Urol 139:74–80Google Scholar
- Von Hayek H (1960) Das Faserkaliber in den Mm. transversus perinei und sphincter urethrae. Z Anat Entwicklungsgesch 121:445–458Google Scholar