Evidence for a propulsive function of the migrating myoelectric complex in rats

In order to investigate the relation between myoelectric activity and the transport of small bowel luminal contents, recordings of migrating myoelectrical complexes (MMCs) were combined with studies of the propulsion of a bile-excreted radioactive test substance. At laparotomy, rats were provided with three pairs of bipolar electrodes, sewn to the seromuscular layer of the small bowel 15, 30 and 45 cm distal to the pylorus. After recovery for 1 week MMCs were recorded with the animal fasted for 18 h and in light barbiturate anesthesia. Concurrently, the bile-excreted radiopharmaceutic, 99mTc-Solco-HIDA, was infused intravenously. At the end of the experiment the rats were sacrificed and the distribution of 99mTc activity was recorded from the excised bowel specimen. In 12 animals with a typical MMC activity recurring every 20 min, the small bowel radioactivity was distributed into discrete portions, separated by fairly long empty segments. In 6 animals the experiments were terminated when an MMC activity front had reached one of the electrodes and in all, a portion of radioactivity was found to be located immediately distal to the position of that particular electrode. 6 control animals were killed when about 10 min had elapsed since the MMC front passed one of the electrode sites. In all these cases the electrode position was found to correspond to empty bowel segments. These data obtained from animals with permanent electrodes but an otherwise intact small bowel strongly support the notion that MMCs result in propulsion of luminal contents.