title: Opioidergic effects on enteric and sensory nerves in the lower GI tract: basic mechanisms and clinical implications.
abstract: Opioids are one of the most prescribed drug classes for treating acute pain. However, chronic use is often associated with tolerance as well as debilitating side effects, including nausea and dependence, which are mediated by the central nervous system, as well as constipation emerging from effects on the enteric nervous system. These gastrointestinal (GI) side effects limit the usefulness of opioids in treating pain in many patients. Understanding the mechanism(s) of action of opioids on the nervous system that shows clinical benefit as well as those that have unwanted effects is critical for the improvement of opioid drugs. The opioidergic system comprises three classical receptors (μ, δ, κ) and a nonclassical receptor (nociceptin), and each of these receptors is expressed to varying extents by the enteric and intestinal extrinsic sensory afferent nerves. The purpose of this review is to discuss the role that the opioidergic system has on enteric and extrinsic afferent nerves in the lower GI tract in health and diseases of the lower GI tract, particularly inflammatory bowel disease and irritable bowel syndrome, and the implications of opioid treatment on clinical outcomes. Consideration is also given to emerging developments in our understanding of the immune system as a novel source of endogenous opioids and the mechanisms underlying opioid tolerance, including the potential influence of opioid receptor splice variants and heteromeric complexes.
authors.affiliation: Centre for Nutrition and Gastrointestinal Disease, Department of Medicine, University of Adelaide and South Australian Health and Medical Research Institute, Adelaide, South Australia, Australia; School of Medicine, Faculty of Health Sciences, University of Adelaide, Adelaide, South Australia, Australia; patrick.hughes@adelaide.edu.au.
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Hughes
authors.affiliation: School of Medicine, Faculty of Health Sciences, University of Adelaide, Adelaide, South Australia, Australia; Department of Gastroenterology and Hepatology, Royal Adelaide Hospital, Adelaide, South Australia, Australia; and Department of Gastroenterology, The Queen Elizabeth Hospital, Woodville, South Australia, Australia.
authors.forename: Samuel P
authors.initials: SP
authors.lastname: Costello
authors.affiliation: School of Medicine, Faculty of Health Sciences, University of Adelaide, Adelaide, South Australia, Australia; Department of Gastroenterology and Hepatology, Royal Adelaide Hospital, Adelaide, South Australia, Australia; and.
authors.forename: Robert V
authors.initials: RV
authors.lastname: Bryant
authors.affiliation: School of Medicine, Faculty of Health Sciences, University of Adelaide, Adelaide, South Australia, Australia; Department of Gastroenterology and Hepatology, Royal Adelaide Hospital, Adelaide, South Australia, Australia; and.
authors.forename: Jane M
authors.initials: JM
authors.lastname: Andrews
mesh_terms: D000698:Analgesia; D000701:Analgesics, Opioid / Q000494:pharmacology*; D005767:Gastrointestinal Diseases / Q000188:drug therapy*; D006801:Humans; D041741:Lower Gastrointestinal Tract / Q000294:innervation*; D011957:Receptors, Opioid / Q000378:metabolism*
chemical_list: D000701:Analgesics, Opioid; D011957:Receptors, Opioid
keywords: immune; inflammatory bowel diseases; irritable bowel syndrome; nervous system; opioid