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 α2 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. (C) 2000 by Am. Coll. of Gastroenterology.
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