IntroductionNonobstructive ileus, signifying the impairment of coordinated propulsive intestinal motility, remains a frequently documented and almost inevitable consequence of open abdominal surgery and sepsis. Animal models suggest that both neuronal and local inflammatory responses are involved. Altered sensory mechanisms are believed to contribute but this has not been investigated directly. Here we describe the results of an in vitro electrophysiological study of mesenteric afferent sensitivity in jejunal segments from mice during postoperative ileus.MethodC 57 BL/6 mice were anaesthetized with enflurane inhalation and at laparotomy the small bowel was either manipulated to induce ileus or left untouched (sham controls). 24 h later, 2 – 3 cm segments of jejunum with mesenteric arcade attached were removed and bathed in Krebs buffer at 34°C. Extracellular multi-unit mesenteric afferent recordings were made from one paravascular nerve bundle during luminal ramp distension with saline (0.5 ml/min up to a maximum pressure of 60 mmHg) and during intraluminal administration of the inflammatory mediators 5-HT, histamin and bradykinin. Afferent responses to stimulation are quoted as mean discharge frequency over baseline and expressed as mean (imps−1) ± SEM. Data have been compared using Students’ t-tests.ResultsSegments of ileus bowel were dilated and flaccid while sham controls showed phasic increases in intraluminal pressure. There was a significant difference between ileus and sham segments in spontaneous discharge (17 ± 1 vs. 12 ± 2 imp/s, P = 0.02, N = 6), but not in the peak response to ramp distension (maximum △ at 60 mmHg = 85 ± 6.0 vs. 70 ± 4 imp/s respectively, P = 0.07). However, the afferent response profile was different in ileus compared to sham control with a significantly increased response at low distending pressures (2–20 mmHg) compared to sham control (19 ± 2 vs 9 ± 2 imp/s, P < 0.05). The distending volume at 60 mmHg was similar in postoperative ileus animals and controls (0.44 ± 0.08 vs 0.36 ± 0.02 ml). In sham operated animals 5-HT (9 ± 1 imp/s, N = 36) and bradykinin (11 ± 2 imp/s, N = 2) elicited an increase in mean discharge rates as did Histamin (6 ± 1 imp/sec, N = 2). This was unchanged after the induction of ileus (5-HT 7 ± 3, N= 3, bradykinin 13 ± 6, N= 3, histamin 4 ± 2, N = 4, all P > 0.05; unpaired t-test).ConclusionInflammatory mediators are activating afferent intestinal nerve fibers, however, in this pilot study, the response was unchanged during ileus, while jejunal motility was inhibited. Afferent mechanosensitivity appears to be increased during postoperative ileus at low distending pressures which may be secondary to afferent sensitization by locally released inflammatory mediators.