title: Expression and physiology of opioid receptors in the gastrointestinal tract.
abstract: OBJECTIVE
  Stimulation of opioid receptors elicits analgesic effect not only in the central nervous system, but also in the gastrointestinal tract, where a high concentration of opioid receptors can be found within the enteric nervous system as well as muscular and immune cells. Along with antinociception, opioid receptors in the stomach and intestine relay signals crucial for secretory and motor gastrointestinal function.
  
  
  RESULTS
  The review focuses on the utility of opioid receptor antagonists, which is generally contributing to the management of postoperative ileus and opioid bowel dysfunction in chronic pain patients nonetheless, opioid receptor antagonists can also be useful in the treatment of irritable bowel syndrome and chronic idiopathic constipation. The study also discusses several antidiarrheal opioid agonists, as well as opioids and opioid mimetics encompassing the concept of ligand-biased agonism and truncated opioid receptor splice variants.
  
  
  CONCLUSIONS
  Good understanding of the localization and the role of opioid receptors is vital for regulation of various pathophysiological processes in the gastrointestinal tract and may simultaneously provide a tempting approach in eliminating adverse effects related to centrally acting opioids.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, Medical University of Lodz, Lodz, Poland.
authors.forename: Paula
authors.initials: P
authors.lastname: Mosińska
authors.forename: Marta
authors.initials: M
authors.lastname: Zielińska
authors.forename: Jakub
authors.initials: J
authors.lastname: Fichna
mesh_terms: D005767:Gastrointestinal Diseases / Q000188:drug therapy*; D041981:Gastrointestinal Tract / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D009292:Narcotic Antagonists / Q000494:pharmacology*; D011957:Receptors, Opioid / Q000378:metabolism / Q000502:physiology*
chemical_list: D009292:Narcotic Antagonists; D011957:Receptors, Opioid