Opioids: Difference between revisions

Opioids are known to mimic endogenous endorphins. Endorphins are responsible for analgesia (reducing pain), causing sleepiness, and feelings of pleasure. They can be released in response to pain, strenuous exercise, orgasm, or excitement. This mimicking of natural endorphins results in the drug's [[Physical euphoria|euphoric]], [[Pain relief|analgesic]] (pain relief) and [[Anxiety suppression|anxiolytic]] (anti-anxiety) effects.<ref>{{cite journal | vauthors = Boecker H, Sprenger T, Spilker ME, Henriksen G, Koppenhoefer M, Wagner KJ, Valet M, Berthele A, Tolle TR | title = The runner's high: opioidergic mechanisms in the human brain | language = en | journal = Cerebral Cortex | volume = 18 | issue = 11 | pages = 2523–31 | date = November 2008 | pmid = 18296435 | doi = 10.1093/cercor/bhn013 }}</ref>

Opioids act on the three main classes of [[opioid receptor]] in the nervous system, μ, κ, δ (mu, kappa, and delta).<ref name="receptors">Opioid - Chapter 2: The Endogeneous Opioid Systems

(http://www.stoppain.org / Beth Israel Medical Center's Department of Pain Medicine and Palliative Care) | https://web.archive.org/web/20110719072413/http://www.stoppain.org/pcd/_pdf/OpioidChapter2.pdf</ref> Each opioid is measured by its [[agonist]]ic or [[antagonist]]ic effects towards the receptors, with the responses to the different receptor sub-types (e.g., μ1 and μ2) providing even more effects. Opioid receptors are found mainly within the brain, but also within the spinal cord and digestive tract.<ref>Opioid receptors in the gastrointestinal tract

The delta receptor is responsible for the [[analgesia]], antidepressant and convulsant effects as well as physical dependence.<ref name="receptors"/>

The kappa receptor is responsible for the [[analgesia]], [[anticonvulsant]], [[dissociative]] and [[deliriant]] effects as well as dysphoria, neuroprotection and [[sedation]].<ref name="receptors"/>

The mu receptor is responsible for [[analgesia]], physical dependence, [[respiratory depression]], [[euphoria]], and possible [[vasodilation]].<ref name="receptors"/>

The nociceptin receptor is responsible for [[anxiety]], [[depression]], appetite and development of tolerance to μ agonists.<ref name="pmid10742280">{{cite journal | vauthors = Calo' G, Guerrini R, Rizzi A, Salvadori S, Regoli D | title = Pharmacology of nociceptin and its receptor: a novel therapeutic target | journal = British Journal of Pharmacology | volume = 129 | issue = 7 | pages = 1261–83 | date = April 2000 | pmid = 10742280 | pmc = 1571975 | doi = 10.1038/sj.bjp.0703219 }}</ref><ref>{{cite journal | vauthors = Toll L, Bruchas MR, Calo' G, Cox BM, Zaveri NT | title = Nociceptin/Orphanin FQ Receptor Structure, Signaling, Ligands, Functions, and Interactions with Opioid Systems | journal = Pharmacological Reviews | volume = 68 | issue = 2 | pages = 419–57 | date = April 2016 | pmid = 26956246 | doi = 10.1124/pr.114.009209 | url = http://pharmrev.aspetjournals.org/content/68/2/419 }}</ref>

 

====='''Zeta (ζ)'''=====

The zeta opioid receptor, also known as opioid growth factor receptor (OGFr) is responsible for tissue growth, neural development, and is further implicated in the development in some cancers.<ref name="pmid10519055">{{cite journal | vauthors = Zagon IS, Wu Y, McLaughlin PJ | title = Opioid growth factor and organ development in rat and human embryos | journal = Brain Res. | volume = 839 | issue = 2 | pages = 313–22 |date=August 1999 | pmid = 10519055 | doi = 10.1016/S0006-8993(99)01753-9  | url =  | issn = }}</ref><ref name="pmid12854052">{{cite journal | vauthors = Sassani JW, Zagon IS, McLaughlin PJ | title = Opioid growth factor modulation of corneal epithelium: uppers and downers | journal = Curr. Eye Res. | volume = 26 | issue = 5 | pages = 249–62 |date=May 2003 | pmid = 12854052 | doi = 10.1076/ceyr.26.4.249.15427| url = | issn = }}</ref><ref name="pmid10024694">{{cite journal | vauthors = Zagon IS, Smith JP, McLaughlin PJ | title = Human pancreatic cancer cell proliferation in tissue culture is tonically inhibited by opioid growth factor | journal = Int. J. Oncol. | volume = 14 | issue = 3 | pages = 577–84 |date=March 1999 | pmid = 10024694 | doi = 10.3892/ijo.14.3.577| url = | issn = }}</ref><ref name="pmid10200353">{{cite journal | vauthors = McLaughlin PJ, Levin RJ, Zagon IS | title = Regulation of human head and neck squamous cell carcinoma growth in tissue culture by opioid growth factor | journal = Int. J. Oncol. | volume = 14 | issue = 5 | pages = 991–8 |date=May 1999 | pmid = 10200353 | doi = 10.3892/ijo.14.5.991| url = | issn = }}</ref><ref name="pmid17974995">{{cite journal |vauthors=Cheng F, Zagon IS, Verderame MF, McLaughlin PJ |title=The opioid growth factor (OGF)-OGF receptor axis uses the p16 pathway to inhibit head and neck cancer |journal=Cancer Research |volume=67 |issue=21 |pages=10511–8 |date=November 2007 |pmid=17974995 |doi=10.1158/0008-5472.CAN-07-1922 |url= |issn=}}</ref><ref name="pmid19297547">{{cite journal |vauthors=Donahue RN, McLaughlin PJ, Zagon IS |title=Cell Proliferation of Human Ovarian Cancer is Regulated by the Opioid Growth Factor - Opioid Growth Factor Receptor Axis |journal=American Journal of Physiology. Regulatory, Integrative and Comparative Physiology |volume= 296|issue= 6|pages= R1716–25|date=March 2009 |pmid=19297547 |doi=10.1152/ajpregu.00075.2009 |url= |issn=}}</ref> The endogenous ligand for OGFr is met-enkephalin, which is also a powerful endogenous delta opioid receptor agonist.<ref name="Stein1999">{{cite book | author = Christoph Stein | title = Opioids in pain control: basic and clinical aspects | url = https://books.google.com/books?id = 4Rfr8cQayvgC&pg = PA22 | accessdate = 25 November 2011 | year = 1999 | publisher = Cambridge University Press | isbn = 978-0-521-62269-1 | pages = 22–23}}</ref>