BACKGROUND: Our aim was to explore unknown changes in neurotransmission with vasoactive intestinal peptide (VIP) and Substance P (Sub P) during postoperative ileus (POI). METHODS: Contractile activity of rat circular jejunal muscle strips was studied in five groups (n = 6/group): Naïve controls, sham controls 12 h and 3 days after laparotomy, and rats 12 h, 3 days after induction of POI. Dose-responses to VIP (10(-10) -10(-7) M), Sub P (3 × 10(-10) -3 × 10(-7) M), and electrical field stimulation (EFS, to study endogenous release of neurotransmitters) were studied with different antagonists. Intestinal transit, inflammatory cells and immunoreactivity for VIP and Sub P were investigated in the bowel wall and cellular Finkel osteo sarcoma expression was determined in vagal afferent and efferent nuclei of the brainstem. KEY RESULTS: Postoperative ileus characterized by delayed intestinal transit and intramural inflammation was associated with an increased inhibitory effect of VIP on contractile activity. A biphasic impact was observed for Sub P with a decrease in its excitatory potential on contractility at 12 h, followed by a later increase 3 days postoperatively. Inhibitory response to EFS was increased, whereas the excitatory response decreased in ileus animals. VIP expression was increased in all postoperative animals while only animals 3 days after ileus induction showed increased Sub P expression in the myenteric plexus. These changes were associated with an activation of afferent but not efferent vagal nuclei in the brain stem. CONCLUSIONS & INFERENCES: Specific, time-dependent changes in peptidergic neurotransmission with VIP and Sub P occur during POI that are associated with vagal afferent activation, but are independent of the activation of efferent vagal pathways.