Acute and chronic responses associated with adrenomedullin administration in experimental colitis

Adrenomedullin (AM) is a 52 amino acid peptide and member of the calcitonin gene-related peptide (CGRP) super family. Given that AM has emerged as a potential immuno-regulatory and anti-inflammatory agent in various experimental models, this study has deepened into its possible therapeutic effect in intestinal inflammation analyzing the responses in both acute and chronic (14 and 21 days) phases of TNBS-induced colitis in rats. In the acute model, AM treatment reduced the incidence of diarrhea and the severity of colonic damage, and improved the survival rate at the three doses assayed (50, 100, and 200 ng/kg animal). AM administration was able to reduce the early production of TNF-α and collaborated to maintaining basal levels of IFN-γ and IL-10. In the chronic studies the peptide attenuated the extent of the damage with lesser incidence of weight loss and diarrhea (50 and 100 ng/kg animal). Cellular neutrophil infiltration, with the subsequent increase in myeloperoxidase (MPO) levels caused by TNBS, was reduced after chronic AM administration. The peptide played a role in the evolution of Th1/Th2 cytokines balance and chronic disease recuperation: levels of proinflammatory TNF-α and IFN-γ decreased and anti-inflammatory IL-10 increased significantly. Cyclooxygenase-2 (COX-2) and nitric oxide synthase (iNOS) protein expression were not modified by AM administration, although a reduction of nitric oxide (NO) production could be detected in the chronic model. These results support a role of AM as an anti-inflammatory factor with beneficial effects in intestinal inflammatory colitis.