The effect of small intestinal transplantation on intraluminal levels of serotonin and substance P.

This study was performed to examine the effect of transplantation, and thus extrinsic denervation, of the small intestine on intraluminal release of serotonin and substance P. Heterotopic 40-cm-long proximal (jejunal) small intestinal isografts were performed in six 200- to 250-g adult male Lewis rats under general anesthesia. Bowel ends were exteriorized as ostomies. Six Lewis rats with neurovascularly intact 40-cm proximal small bowel Thiry-Vella loops exteriorized as ostomies served as the control animals. On the seventh postoperative day, the intestinal loops were perfused at 0.5 ml/min for three 10-min periods with normal saline followed by an equilibrium period and then for three 10-min periods with 20% dextrose. Perfusates were collected for each period and levels of serotonin and substance P were determined by radioimmunoassay. Intraluminal serotonin levels rose from 29 +/- 9 ng/ml during saline perfusion to 115 +/- 28 ng/ml during intestinal perfusion with 20% dextrose in the innervated loops and from 21 +/- 7 ng/ml to 94 +/- 26 ng/ml in the transplanted loops. While there was a statistically significant increase in mean intraluminal serotonin levels following perfusion with 20% dextrose in both the control and transplant groups, there was no difference in the intraluminal serotonin response between controls and transplant recipients. In contrast, 20% dextrose had no effect on luminal release of substance P in either group. These results indicate that extrinsic denervation of the small intestine has no effect on the intraluminal serotonin response to stimulation and suggest that serotonin and substance P are not released into the intestinal lumen by the same regulatory mechanisms.