The mechanisms by which a fatty meal alters small bowel motility was studied in rats. The fatty meal (3 ml soya bean emulsion) was infused via a permanent gastric catheter and, simultaneously, a bile-excreted radiopharmaceutic, via a central venous catheter. After infusion for 1 h the radioactivity along the small bowel was measured from the excised bowel specimen. In fasting animals an ‘interdigestive’ pattern was found, characterized by the distribution of small bowel contents in well-separated portions. After administration of the fat meal, a different (‘postprandial’) type of transit was found, characterized by a continuous distribution of radioactivity along the small bowel. In vagotomized animals the chosen fat meal did not induce a postprandial pattern but instead the small bowel retained its interdigestive transit mode. However, in intact animals pretreated with atropine or naloxone, the fatty meal intragastrically resulted in an ordinary postprandial transit pattern. Thus, the effect of the surgical vagotomy seems to be mediated by interruption of noncholinergic, nonenkephalinergic neurons.
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.
A method is presented for studies of small bowel propulsion in conscious rats with an intact gastrointestinal tract. A bile-excreted test substance, 99Tcm-Solco-HIDA, was infused intravenously for time periods varying between 0.25 and 5 h. Immediately after the infusion, radioactivity was recorded from the excised bowel specimen. The activity distribution along the small bowel was always found to be ‘peaky’, i.e. the intestinal contents were transported in portions separated by fairly long completely empty regions. In a control experiment with simultaneous intravenous infusion of 99Tcm-Solco-HIDA and infusion of a nonabsorbable test substance (12SI-PVP) through a permanent duodenal catheter a similar activity distribution was observed. This indicates that the peaky appearance of the activity distribution is not due to a periodicity in the discharge of bile but reflects small bowel propulsive activity.
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