A comparison of small intestinal transit time between the rat and the guinea-pig.

The small intestinal transit was compared in rats and guinea-pigs. A radioactive test substance (polyvinylpyrrolidone labelled with I125) was given directly into the duodenum and the distribution of the isotope in the small bowel was recorded. The small intestine was removed 10 and 20 min after the injection and deep frozen. The frozen intestine was later cut in 20 segments of equal length and the amount of isotope within each of the intestinal segments was recorded by means of a gamma counter. For each animal a propulsion diagram was constructed showing the relative percentage of isotope distributed in the 20 bowel segments. After 20 min the isotope peak was found in the ileo-caecal region in the guinea-pigs whereas 50% of the isotope had passed only half of the small intestine in the rats during the same period of time. The length of the intestine in rats passed by 75%, 50% and 25% of the isotope after 20 min was the same as that found in guinea-pigs 10 min after the injection of the isotope into the duodenum. Thus, there seems to be a marked difference in propulsive activity between rats and guinea-pigs.