Anorectal Manometry in Wistar Rats with Inexpensive Setup: A Physiological Description of the Mechanical Activity

Abstract

Anorectal manometry is a common technique for investigating the performance of the anal canal. The absence of the rectosphincteric reflex may determine the existence of important pathologies. Animal models are essential to assess the efficacy of new therapies as well as to provide a better understanding of the physiological mechanisms underlying intestinal motility. This paper describes an inexpensive laboratory setup for experimental anorectal manometry that consists of a water-perfused customized catheter, a signal acquisition and processing system, and a personal computer with a software program to display biosignals. Twenty Wistar rats, ten males and ten females, were anesthetized using a ketamine–xylazine intraperitoneal injection. The basal tone of the anorectal sphincter and the rectosphincteric reflex were studied. In basal conditions, two frequency peaks were found, one at 0.015 ± 0.007 Hz and the other at 0.363 ± 0.057 Hz, corresponding to slow and ultraslow pressure waves, respectively. The maximum resting pressure varied between 37.8 and 109.0 mmHg. Anorectal relaxations derived from stimulation of the rectum wall dropped to 82.65 ± 14.61 % of the pressure level prior to stimulation. The overall period of the relaxation wave was 10.22 ± 2.91 s. Differences between genders were found: autonomous pressure oscillations were significantly slower in female rats whereas the period of the relaxation wave was significantly shorter in male subjects. Overall, the mechanical description of the anal canal in Wistar rats is similar to that in humans, especially to that in newborns. Therefore, it represents a good animal model for the investigation of anorectal motility.