PERIODIC RECTAL MOTOR-ACTIVITY - THE INTRINSIC COLONIC GATEKEEPER

Background: Rectal motor activity is incompletely understood, The aim of this study was to characterize the patterns of rectal motor activit y and to examine their diurnal variation and their relationships to pr oximal colonic activity and to meals, Methods: We performed a 30-h amb ulatory motility study by recording pressure activity at multiple site s in the colon in 18 normal subjects, Results: During 288 h of recordi ng, discrete bursts of tonic and phasic activity were seen in the rect um of all subjects at night and during the day lasting greater than or equal to 3 min, with a predominant frequency of 3 waves/min: periodic rectal motor activity (PRMA). Nocturnally, the number of cycles and t he proportion of time occupied by this activity were greater (p < 0.00 1) and the inter-cycle interval was shorter (p < 0.008) compared with daytime, but the cycle duration was similar, Only 4 versus 5% (nocturn al vs daytime) of cycles propagated aborad, whereas 36 versus 14% (p < 0.01) propagated retrogradely, 16 versus 47% (p < 0.01) occurred simu ltaneously, and 44 versus 34% were confined to the rectum, There was c onsiderable intra- and intersubject variability, PRMA was not related to meals or to anal motor activity, but 81% of nocturnal and 94% of da ytime cycles occurred within 5 min of a motor event in the more proxim al colon, Conclusions: PRMA is a characteristic feature of the normal rectum and is more frequent at night, The temporal association with mo tor events in the proximal colon suggests that PRMA is triggered by th e arrival of stool or gas in the rectum, Because most cycles are eithe r segmental or are propagated retrogradely, PRMA may serve as an intri nsic braking mechanism that prevents untimely flow of colonic contents , particularly during sleep.