AIM:To investigate whether peripheral corticotropin releasing hormone (CRH),which is up-regulated in intestinal inflammation,mediates the post-inflammatory visceral hypersensitivity in a rat model of colitis.METHODS:We measured mucosal myeloperoxidase (MPO) activity as a marker of inflammation,plasma CRH level,and abdominal withdrawal reflex (AWR) to colorectal distension as a visceral nociceptive response at 2,7 and 14 d after the induction of colitis with 4% acetic acid.RESULTS:Colonic inflammation,quantified by MPO activity,significantly increased on d 2 and subsided thereafter,which indicated a resolution of inflammation within 7 d.On the contrary,plasma CRH level and AWR score were increased on d 2,remained high on d 7,and returned to control level on d 14.Intraperitoneal injection of a CRH antagonist,astressin (30 μg/kg),significantly attenuated the post-inflammatory visceral hypersensitivity on d 7.Furthermore,intraperitoneal administration of CRH (3 and 10 μg/kg) mimicked the post-inflammatory visceral hypersensitivity in naive rats.CONCLUSION:These results suggest that increased peripheral CRH mediates the enhanced visceral nociception in rats recovered from experimental colitis.