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 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 show clinical benefit as well as those that have unwanted effects is critical for the improvement of opioid drugs. The opioidergic system comprises 3 classical receptors (µ,δ, κ) and a non-classical receptor (Nociceptin) and each of these receptors are 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 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 opioid treatment has 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.
- nervous system
- Irritable Bowel Syndrome
- Inflammatory Bowel Diseases
- Copyright © 2015, American Journal of Physiology- Gastrointestinal and Liver Physiology