Objective: To clarify the muscle fibre types in the striated urethral sphincter and the pattern of distribution of this muscle in the prostatic capsule.
Materials and methods: Twenty-three prostate glands obtained at radical prostatectomy were studied using a whole-organ technique. Each gland was sectioned from prostatic apex to base, including the bladder neck and seminal vesicles. The slides were then traced on paper after staining with haematoxylin and eosin and the distribution of striated muscle mapped. Two prostates were studied after sectioning with a cryostat and staining with adenosine phosphatase at pH 4.2, 4.6 and 4.93 to distinguish between the sub-classification of Type 2 fibres. Other sections were stained for nicotinamide adenine dinucleotide phosphate with nitroblue tetrazolium, to distinguish fast from slow twitch fibres.
Results: Striated muscle was present within the anterolateral aspect of the prostatic capsule, extending from the prostatic apex to the bladder neck. Three different fibre types were present; fast-twitch fatigue-sensitive, fast-twitch fatigue-resistant and slow-twitch.
Conclusion: There are three distinct fibre types in the prostatic capsular striated muscle, representing displaced muscle fibres from the striated urethral sphincter. The composition of three types makes it eminently suitable to function as a sphincter muscle.