Histochemical Study of Urethral Striated Musculature in the Dog

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Abstract
The striated musculature of the dog urethra was studied histochemically. Two main groups of muscle fibers could be identified: 1 with slow twitch oxidative fibers, which are fatigue resistant (type 1), and 1 with fast twitch fibers (type 2). The fast twitch fibers were subdivided into glycolytic (fatiguable) and oxidative glycolytic (fatigue resistant) fibers: the latter constitute 20% of all fast twitch fibers. Type 1 constitutes 35% of the whole musculature and its proportion tends to decrease toward the distal end of the external urethral sphincter. Apparently, type 1 fibers are likely to be responsible for continence at rest and type 2 fibers are recruited in stress conditions, for example, during coughing or sneezing. Additional studies are needed to confirm this conjecture. The clinical implications of these studies [in humans] for the control of incontinence, urinary retention and dyssynergic urethral sphincter are presented.