Anatomical Features of Male Rat Urethra and Comparison of Urethral Sphincter Contractility according to Different Urethral Strip Orientations

Jung, Woong Gyo; Cho, Su Yeon; Lee, Ji Youl

Abstract

PURPOSE: The aim of the study was to clarify the anatomy of the male rat urethra, and to establish a more accurate and consistent method for analyzing external urethral sphincter (EUS) contractility based on this clarified anatomy by comparing different muscle strip orientations.
MATERIALS AND METHODS
The whole urethra in male rats was investigated histologically using H/E and immunohistochemical staining. The contractility of the spiral (S) orientation of the entire proximal urethral (EUS) was then compared with the transverse (T) and the ring (R) orientations of the optimal portion, via electrical stimulation in an organ bath.
RESULTS
In male rats, the urethral tract consisted of following parts: proximal urethra, transient urethra, urethral diverticula, and penile urethra. Throughout the proximal urethra, a layer of striated muscle fibers encircled the smooth muscle layers. The EUS contraction of the S, TM (Transverse, Middle of proximal urethra) and RM (Ring, Middle of proximal urethra) groups were 4.66+/-0.33mN, 2.92+/-0.33mN and 2.47+/-0.38mN, respectively. The strength of the EUS contraction of the S group was significantly higher than that of the TM. Group, but after adjusting the length, there was no statistically significant difference between the two groups.
CONCLUSIONS
Unlike previous studies, showing striated muscle fibers limited to the lower half of the proximal urethra, we noted them throughout the whole proximal urethra. From our results, the spiral orientation of the entire urethra was found to be the optimal configuration for evaluating the contractility of the EUS using fast twitch muscle contractile testing.