Anatomical and Histological Analysis of the Urethral Vascular System in Female Rats

There exists a complex vascular structure within the female urethra, and these structures may be closely related to urinary continence. Therefore, the overall anatomical structure of the urethra at the macroscopic scale still requires further clarification. We hypothesized that a specialized musculo-vascular complex exists within the female mid-urethra, which could be visualized and characterized using advanced 3D imaging techniques.

Nine Sprague-Dawley rats (6 females, 3 males for preliminary comparison) and 2 canines were used. The primary aim was to provide a high-resolution 3D anatomical description of the female rat urethra, with a specific focus on the vascular-muscular system. To achieve this, we employed fMOST, Masson's Trichrome staining, 3D immunolabeling, vessel labeling, tissue clearing, light-sheet microscopy, and immunofluorescence staining.

The vascular architecture of the female rat urethra demonstrates remarkable complexity. In the mid-urethral segment, a venous sinus forms an intricate reticular network. This vascular plexus exhibits two distinct structural components: one is enveloped by the surrounding striated musculature, whereas the other closely apposes the urethral lumen and is structurally positioned to potentially contribute to suggesting a potential contribution to urethral closure mechanisms, a hypothesis requiring functional validation. These components are interconnected via anastomotic reticular branches, forming a structurally integrated system that is anatomically poised to function as a unit. This specialized anatomical configuration may play a role in urinary continence, a hypothesis that now requires functional testing. Similar vascular architectures have been documented across mammalian species, suggesting evolutionary conservation of this structure-function relationship.

This study provides the first 3D depiction of the urethral vascular-muscular complex, revealing a highly specialized anatomical structure in the female rat mid-urethra. Based on this novel anatomy, we propose the hypothesis that this complex could facilitate urinary continence via a hydraulic mechanism, a premise that now requires direct functional testing in future work.