Objective: The rectoanal inhibitory reflex facilitates defecation by relaxation of the internal anal sphincter during rectal distention by gas or stool. Defecation is sometimes preceded by high-amplitude propagated contractions (HAPCs). Our objective was to seek evidence for motor coordination between human colonic and anal sphincter functions.
Methods: As part of a study of alpha2 modulation of colonic and anal motor functions in 32 healthy volunteers, we studied the relationship between high HAPCs and anal sphincter pressure with colonic manometry, barostat, and a Dent sleeve in the anal canal.
Results: Twenty-two HAPCs were observed; in 19/22 HAPCs there was optimal positioning of the Dent sleeve to assess the anal sphincter. Eighteen of 19 HAPCs occurred postprandially; 14 HAPCs occurred after administration of yohimbine, three after clonidine, and one before any drug administration. Seven followed experimental balloon distention. Anal sphincter relaxation occurred (14 +/- 4 s) before the recorded onset of HAPC in the descending colon and 88 +/- 7 s before the arrival of the HAPC in the rectum. After or during the HAPCs, anal sphincter pressure decreased by 40 +/- 4% and increased by 56 +/- 8% in the postrelaxation phase.
Conclusions: The close temporal association between anal sphincter relaxation and onset of HAPC in the descending colon suggests a coloanal reflex that may facilitate defecation during mass movements independently of the rectoanal inhibitory reflex.