Simultaneous measurement of the propulsion and mixing of small bowel contents in the rat.

A method is presented for the simultaneous measurement of propulsion and mixing of small bowel contents in conscious rats. Through a permanent duodenal catheter two differently labeled test substances (125I-PVP and 131I-PVP) were infused continuously one after the other. The radioactive label was changed once during the total infusion period of 5 hours. Studies were performed in six groups of animals which differed with respect to time for interchange of test substance. At the end of the total infusion period the border zone had travelled to six different locations in the small bowel. The animals were then killed and the two radioactivities were recorded from the excised bowel specimen. The resulting activity densities along the small bowel were peaky and the overlap between the two labels in the border zone was minute, indicating that the intestinal contents were transported in isolated portions with only minor exchange of luminal contents between adjacent regions. The transport apparently proceeded steadily in a mainly aboral direction with no indications of abrupt changes in transport velocity.