Intestinal distension alters vagal efferent activity and small intestinal transport in vivo

We investigated whether intestinal distension altered net water absorption by an adjacent noncontiguous segment of intestine and the mechanism for this effect. Influx and efflux catheters were placed in two intestinal loops, after which the bowel was transected between the loops. During perfusion with Ringers-HCO3-, the proximal loop efflux catheter was elevated 5, 10, or 15 cm above the plane of the rat. Net water absorption was measured in the nondistended caudal (control) loop. Elevation of the proximal loop efflux catheter caused distension and increased intraluminal pressure in this loop but did not alter the circumference or intraluminal pressure of the caudal loop. Distension increased net water absorption by the caudal loop if the vagi were intact and the splanchnic nerves transected. Afferent vagotomy prevented the distension effect. Using the intracellular recording technique, we were able to show that the increase in absorption resulted from a reduction in the activity of vagal neurons innervating the gastrointestinal tract. Intestinal distension reduced the neural activity of 24 of 26 vagal efferent neurons. Our results demonstrate that after splanchnectomy intestinal distension activates a neural circuit that includes afferent and efferent vagal fibers, resulting in increased water absorption.