Effect of myogenic stem cells on the integrity and histomorphology of repaired transected external anal sphincter

Introduction and hypothesis: The objective was to evaluate the effect of myogenic stem cells on histological properties and the volume of striated muscle of the external anal sphincter after transection and repair. Methods: Histological analysis was performed on the external anal sphincters of 40 young female rats euthanized at 7 or 90 days after transection and repair and randomization to injection of either phosphate buffered solution (PBS) or myogenic stem cells (SC) at the transection site. Sphincter complexes, previously evaluated for neurophysiological function, were processed for histology and analyzed for possible disruption, amount of inflammation, and volume of striated muscle. The relationship between the muscular disruption and contractile force of sphincters was evaluated. Results: Disruption was seen in 100 % of sphincters 7 days after repair for both SC and control animals. Eighty-nine percent of controls and 78 % of SC-administered animals had intact sphincters at 90 days. Significant inflammatory infiltrate was seen in repaired anal sphincters for both the PBS and the SC groups at 7 days, and persisted at 90 days, with no difference between treatment groups. Striated muscle volume increased from 7 to 90 days for both control and SC-administered animals. Although there was no difference in volume between treatments, there was substantial temporal improvement in contractile force generation of the sphincters receiving SC compared with those receiving PBS. Conclusion: In this animal model, administration of myogenic stem cells to transected/repaired anal sphincters did not alter the amount of inflammation nor the volume of striated muscle, suggesting that stem cells might improve contractile function through other cellular processes.