Extraordinary muscular structure leads to urethral injury after vaginal delivery in animal study

Exploring the dynamics of progenitor cells in the urethra after simulated birth trauma in mice

OBJECTIVE

To examine the alteration in the cellular dynamics of the urethral tissue after a simulated birth trauma in a mouse model.

MATERIALS AND METHODS

A total of 36 B6 mice received vaginal distention treatment, and four untreated mice were used as controls. Specimens were collected every 24 hours after the injury for 9 consecutive days and examined using immunofluorescent staining for cell markers including c-kit, smooth muscle actin (SMA), and vimentin. Confocal microscopy was used to localize the stained cells and determine the cell number.

RESULTS

The number of c-kit positive cells increased after the 1^st day and peaked on the 3^rd day. The amount of SMA positive cells rapidly reduced to its lowest count on the 1^st day and maintained a statistically significant low cell number than that at the basal level for 4 days after vaginal distension. The cell number finally returned to basal level on the 9^th day. The amount of vimentin positive cells increased dramatically after the 1^st day and plateaued from the 3^rd day to the 9^th day. The number of vimentin positive cells in the plateau phase was significantly higher than that of the control group.

CONCLUSION

Our study confirmed that the dynamic change in different cell types after the urethral injury was dependent on the nature and physiology of the wound repairing cells during the tissue healing process. It might be a simple animal model to study birth trauma repair; however, the varied progenitor cell activity in different species should also be considered.

Paraurethral striated muscular structures and pelvic floor muscles contribute to resting urethral closure pressure in rats

INTRODUCTION AND HYPOTHESIS

We investigated physiological functions of the extraordinary muscular structure in the paraurethral area with pelvic floor muscle and the impact of these muscular structures on the resting maximal urethral closure pressure (MUCP) in rats.

METHODS

Sixteen female Wister rats were divided into four groups: Groups I and II rats received 5 and 2.5 IU botulinum toxin A (BoNT-A), respectively, injected into the bilateral paraurethral striated muscles. Group III rats received 2.5 IU BoNT-A injected into the bilateral pelvic floor muscles, and group IV rats received 2.5 IU BoNT-A injected into the unilateral pelvic floor muscles. Measurements of MUCP were made at different time points after BoNT-A injection.

RESULTS

All groups showed a rapid reduction in average MUCP by 70-80 % after BoNT-A injection, regardless of injection site or side.

CONCLUSIONS

Paraurethral striated muscular structures and the pelvic floor muscles possess the function of maintaining resting MUCP in rats.