(Purpose) A comparative study about the contractility of the external urethral sphincter in the pelvic floor muscle (PFM) and about that of the periurethral striated sphincter (PUS), which is independent of PFM, was made by employing adult male mongrels. (Methods) This study was done by using the compression-time curve. Moreover, the study about the formation of muscle fibers was carried out by the aid of ATPase staining. (Results) Stimulus to one side of pudendal nerve increased each sphincter M-wave amplitudes and its compressive differences in contraction. Easy repetitions of the experiment made it possible to use the compression-time curve. The compressive differences in the urethral contraction was significantly greater in the urethra of PUS than in that of PFM. Data obtained from the compressive-time curve showed PUS premotor time was significantly longer than PFM in electromyograms, PUS motor time and time to peak force was significantly shorter, and PUS rate of force development was significantly faster. The histochemical study showed that fast muscles account for 70% in PUS, while they account for approximate 50% in PFM, which supported the results of the compression-time curve. (Conclusion) The above suggested the contractility of PUS apparently differed from that of PFM; PUS contracts quickly, while PFM contracts slowly. Also, it seemed that forming conjectures with the compression-time curve on the formation of muscle fibers in the striated urethral sphincters were possible to some degree.
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