Myoelectrical activity and propulsion in the large intestine of fed and fasted rats

Electrical spiking activity of different parts of the colonic wall was studied in relation to the mechanical events in conscious rats fitted with chronically implanted nichrome wire electrodes and miniaturized strain-gauge transducers. The progress of barium sulphate introduced into the caecum and measured radiographically at fixed intervals was used as an index of transit rate of colonic contents in both the fasted and fed state. The basic pattern of colonic myoelectrical activity was characterized by randomly occurring spike bursts at a higher frequency in the proximal (0.9/min) than the distal colon (0.5/min). Their duration in the fasted state, which was shorter in the proximal (5.5 +/- 1.7 s) than the distal colon (12.7 +/- 2.9 s), was similar following a meal. In the fasted state, integrated records showed cyclical periods of more intense electrical activity lasting about 20 and 40 min in the proximal and the distal colon, respectively. The cyclical pattern following a meal occurred at shorter intervals in the different parts of the colon. Conversely, the propulsion of the marker over the whole colon, which lasted 180-200 min, was accelerated by 30% after feeding. Laxatives disrupted these cyclical motor events on the colon, by inducing mass movements which impeded the pellet formation and increased the rate of transit. The cyclical motor activity was also disrupted following the administration of opiate agonists, the rate of transit being decreased and propulsive activity inhibited. The results are consistent with the concept of cyclical motor pattern playing an important part in the control of pellet formation and movement of digestive contents within the colon of the rat.