Effects of pregnancy, parturition, and anal sphincter transection on function of the external anal sphincter in an animal model.
OBJECTIVE
To estimate the effects of pregnancy, parturition, and anal sphincter laceration (with repair) on external anal sphincter morphology and neurophysiology and to define the time course of these effects after injury.


METHODS
Within 4 hours of vaginal delivery, 80 rats underwent either sham or anal sphincter laceration with repair. After 3 days, 3 weeks, and 3 and 6 months (n=20 for each time point), animals were killed, and the anal sphincter complexes dissected and removed for neurophysiologic studies. Twitch tension, peak tetanic force, fatigue, and maximal electrical field-stimulated force generation were determined. Sphincters were then fixed and serially sectioned (5-micrometer thickness) at 100-micrometer intervals for histologic analysis.


RESULTS
Maximal electrical field-stimulated force generation, maximal tetanic contraction, and twitch tension were decreased in the external anal sphincter 3 days after anal sphincter laceration with repair compared with sham-operated parturient rats (3.3 g compared with 11.6 g, 4.5 g compared with 14.5 g, and 0.6 g compared with 2.0 g, respectively, all P<.02). Increased fatigability of the sphincter muscle was observed in all newly parturient rats-sham and anal sphincter laceration with repair; recovery occurred in the shams by 3 months. A gradual recovery occurred in all these neurophysiologic measures, with no significant differences between anal sphincter laceration with repair and shams by 6 months postpartum.


CONCLUSIONS
Repaired anal sphincter transection in periparturient animals results in short-term severe compromise of neurophysiologic function of the external anal sphincter. Over time, however, force generation recovers and approximates that of postpartum rats with intact anal sphincters.
Rahn
David D
DD
From the Divisions of Female Pelvic Medicine & Reconstructive Surgery and Reproductive Endocrinology, Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, Texas; and ProPath Laboratories, Inc., Dallas, Texas.
White
Amanda B
AB
Miller
Rodney T
RT
Word
R Ann
RA
Wai
Clifford Y
CY
D001003:Anal Canal / Q000293:injuries / Q000502:physiology / Q000601:surgery; D000818:Animals; D004195:Disease Models, Animal; D004558:Electric Stimulation; D005260:Female; D022125:Lacerations / Q000473:pathology / Q000601:surgery*; D036801:Parturition / Q000502:physiology*; D011184:Postoperative Period; D011247:Pregnancy / Q000502:physiology*; D011897:Random Allocation; D051381:Rats; D013997:Time Factors; D015599:Trauma Severity Indices