Propulsion and mixing of small bowel contents during exogenous gastrin infusion. An experimental study in rat

The effect of intravenous infusion of Synthetic Human Gastrin I (SHG) on the propulsion and mixing of small bowel contents was studied quantitatively in conscious rats. Radioactive test substances were infused continuously through a permanent duodenal catheter for totally five hours. Two differently labelled, but otherwise identical, test substances were used and one of them (125I-PVP) was infused during the first three hours, the other (131I-PVP) during the remaining two hours. The activity distribution of each isotope along the excised bowel specimen was measured immediately after the end of the infusion. The bowel length passed by the transition point between the nuclides and the region of overlap in the border zone between them were taken as measures of propulsion and mixing, respectively. A significant increase of the serum gastrin level during infusion of SHG was verified by radioimmunoassay. The total small bowel transit time was significantly prolonged during gastrin infusion secondary to a retarded propagation velocity in the distal small bowel. The slower transport rate during gastrin infusion was coupled to a significant increase of the mixing of small bowel contents. These changes in small bowel motility were not apparently due to a concomitant increase of gastrict acid secretion, since pretreatment with a potent H2-receptor blocker, cimetidine, did not abolish them.