Implications of Tachykinins and Calcitonin Gene-Related Peptide in Inflammatory Bowel Disease

Abstract

Calcitonin gene-related peptide (CGRP) and the preprotachykinin A gene-derived peptides substance P (SP) and neurokinin A (NKA) are expressed in extrinsic primary afferent nerve fibres and intrinsic enteric neurons of the gut. The actions of tachykinins on the digestive effector systems are mediated by three different types of tachykinin receptor, termed NK₁, NK₂ and NK₃ receptors, while the gastro-intestinal actions of CGRP are brought about by CGRP₁ and possibly other CGRP receptors. These neuropeptide transmitters are expressed by enteric neurons, intestinal muscle, epithelium and vascular system in a cell-specific manner and enable SP, NKA and CGRP to influence motility, electrolyte and fluid secretion, vascular and immune functions in a peptide- and region-specific fashion. Inflammatory disorders of various aetiology involve changes in the peptidergic innervation of the gut, and inflammatory bowel disease is associated with NK₁ receptor upregulation in intestinal blood vessels and lymphoid structures. Some of these alterations are reproduced in experimental models of gastro-intestinal disease, and there is mounting evidence that an imbalanced function of peptidergic neurons contributes to motor, secretory, vascular and immunological disturbances in intestinal anaphylaxis, infection and inflammation. In a therapeutic perspective it seems conceivable that tachykinin and CGRP receptors antagonists can be employed as spasmolytic, antidiarrhoeal, anti-inflammatory and antinociceptive drugs.