Vasopressin augments TNBS‐induced colitis through enteric neuronal V 1a receptor‐mediated COX‐2‐dependent prostaglandin release from mast cells in mice

BACKGROUND: Inflammatory bowel disease (IBD) is a functional disorder with chronic and relapsing clinical features. Vasopressin (VP) is a hormone responsible for water and stress homeostasis and also regulates gastrointestinal inflammation and motility. We explored whether VP was related to IBD pathogenesis and its possible pathway. METHODS: Colitis was induced by 2,4,6-trinitrobenzenesulfonic acid (TNBS) in mice. The disease activity and colonic damage were evaluated through a scoring system. Locations of the V1a receptor were revealed by immunochemistry method in colon. Ussing chamber technique was performed for the electrophysiological characterization by using rat ileum. The (Arg8 )-Vasopressin (AVP)-evoked short-circuit current (Isc) was recorded in the presence of conivaptan (V1a and V2 receptor antagonist), tolvaptan (V1b receptor antagonist), tetrodotoxin (TTX), atropine, cyclooxygenase (COX) inhibitors (indomethacin, nonspecific COX antagonist; SC560, COX-1 antagonist; NS560, COX-2 antagonist), and a stabilizer of mast cell (cromolyn sodium), respectively. KEY RESULTS: TNBS resulted in the obvious loss of body weight and tissue damages in mice. AVP significantly aggravated the TNBS-induced colitis, which was attenuated by conivaptan but not tolvaptan. V1a receptors were found immunopositive in neurons among the enteric nervous system. AVP evoked a pulsatile response in Isc. Its amplitude, frequency, and cycle duration were around 8-15 µA/cm2 , 10-11 mHz, and 1.5 minutes, respectively. Notably, the AVP-evoked change in Isc was abolished by TTX, atropine, conivaptan, indomethacin, NS560, and cromolyn sodium, respectively. CONCLUSIONS AND INFERENCES: VP-V1a receptor played the proinflammatory role in TNBS-induced colitis by promoting COX-2-dependent prostaglandin release from mucosal mast cells, which was mediated by the cholinergic pathway.