Intraperitoneal capsaicin treatment reduces postoperative gastric ileus in awake rats

Introduction: Postoperative gastric ileus interferes with postoperative recovery of the patients. Previous studies suggest that capsaicin-sensitive afferent neurons are involved in the mediation of postoperative gastric ileus. Methods: A group of rats were equipped with a strain gauge transducer sutured to the gastric wall. Gastric motility was recorded after intraperitoneal injection of capsaicin (0.1 µmol/kg and 1 µmol/kg) or vehicle. The rats were given 2 days of recovery before gastric motility was investigated in a postoperative ileus model. Results: Pretreatment with capsaicin 2 days prior to abdominal surgery significantly increased postoperative gastric motility, with complete recovery of gastric motility at 30 min postoperatively (with the baseline motility index set at 100±4%, the gastric motility index 30–45 min postoperatively was 64±4% for the vehicle, 138±20% for capsaicin 0.1 µmol/kg, and 110±12% for capsaicin 1 µmol/kg: P=0.0008 vehicle vs capsaicin). In contrast, capsaicin treatment 2 h prior to abdominal surgery did not increase postoperative gastric motility (gastric motility index 30–45 min postoperatively was 64±4% for the vehicle and 51±8% for capsaicin 0.1 µmol/kg). The acute intraperitoneal injection of capsaicin decreased gastric motility by about 50–60%, the response lasting for 15–30 min. Conclusions: Intraperitoneal capsaicin treatment 2 days prior to abdominal surgery resulted in immediate recovery of postoperative gastric motility, indicating an important role for serosal visceral afferent nerve fibers in the mediation of postoperative gastric ileus. Possibly, capsaicin or vanilloid (capsaicin) receptor agonists can be used to treat postoperative ileus in the future.