Circadian rhythm of rectal motor complexes

Prolonged rectal pressure recordings have revealed that the rectum exhibits typical bursts of regular pressure waves, also called rectal motor complexes. Although there is consensus regarding the characteristics of rectal motor complexes, their function is poorly understood. Furthermore, data regarding the circadian rhythm of these complexes are either lacking or conflicting. Therefore, we conducted a study to investigate the circadian rhythm of rectal motor complexes in fully ambulant subjects. Because a meal is a powerful and physiologic stimulus to elicit colonic pressure activity, we also studied the effect of a meal on these rectal motor complexes.

Prolonged ambulant anorectal pressure recordings were performed in 12 healthy volunteers (male:female ratio, 6:6; median age, 27 (range, 22-53) years). A total of 139 rectal motor complexes were observed in >300 hours of recording.

All subjects exhibited rectal motor complexes during the daytime, whereas in five subjects, no rectal motor complexes were observed during sleep. The number of rectal motor complexes was significantly lower during sleep (diurnal vs. nocturnal, 8 vs. 1 per subject, P < 0.0001). Furthermore, the duration and peak amplitude of these nocturnal rectal motor complexes were significantly reduced. On the ambulant recordings, the subjects marked a total of 20 meals. During the first 2 hours after these meals, rectal motor complexes were noted in 65 percent of the cases. The postprandial frequency of rectal motor complexes was significantly higher than the overall frequency (2/hour vs. 0.4/hour, P = 0.004).

These findings suggest that sleep results in a reduction of rectal motor activity, whereas a meal provides a stimulus for increased rectal motor activity in fully ambulant subjects.