Morphine opioid receptors

Dynorphin may also influence nociception at the spinal level. The levels of prodynorphin mRNA and immunoreactive dynorphin increase in the chronic inflammatory arthritic model (158). Dynorphin also inhibits morphine or P-endorphin-induced analgesia in naive animals and enhances analgesia in tolerant animals, indicating that this peptide may have a regulatory role in opioid analgesia (159). This effect does not appear to be mediated by a classical opioid receptor, since des-tyrosine dynorphin, which does not bind to opioid receptors, also antagonizes morphine analgesia (160). 

In the strict sense, opiates are drugs which are derived from opium and include the natural products morphine, codeine, thebaine and many semi-synthetic congeners derived from them. In the wider sense, opiates are morphine-like drugs with non-peptidic structures. The old term opiates is now more and more replaced by the term opioids which applies to any substance, whether endogenous or synthetic, pqrtidic or non-peptidic, that produces morphine-like effects through an action on opioid receptors. 

The existence of further alternative transcripts of MOP was postulated by the observation that in knockout mice with disrupted exon 1, heroin but not morphine was still analgesically active. Based on earlier observations that the antagonist naloxazone blocked morphine-induced antinociception but not morphine-induced respiratory depression, a subdivision of the MOP in pi and p2 was proposed. However, no discrete mRNA for each of these MOP subtypes has been found. It is, however, possible that subtypes of MOPs result from heterodimerization with other opioid receptors or by interaction with other proteins. 

Bohn LM, Gainetdinov RR, Lin FT et al (2000) p-Opioid receptor desensitization by (3-arrestin-2 determines morphine tolerance but not dependence. Nature 408 720-723... 

Bleich A, Gelkopf M, Weizman T, et al Benzodiazepine abuse in a methadone maintenance treatment clinic in Israel characteristics and a pharmacotherapeutic approach. Isr J Psychiatry Relat Sci 39 104-112, 2002 Bohn LM, Gainetdinov RR, Lin FT, et al Mu-opioid receptor desensitization by beta-arrestin-2 determines morphine tolerance but not dependence. Nature 408 720— 723, 2000... 

Bond C, LaForge KS, Tian M, et al Single-nucleotide polymorphism in the human mu opioid receptor gene alters beta-endorphin binding and activity possible implications for opiate addiction. Proc Natl Acad Sci U S A 95 9608-9613, 1998 Borron SW, Monier C, Risede P, et al Flunitrazepam variably alters morphine, bu-prenorphine, and methadone lethality in the rat. Hum Exp Toxicol 21 399-603, 2002... 

Lotsch J, Zimmermann M, Darimont J, et al Does the Al 18G polymorphism at the mu-opioid receptor gene protect against morphine-6-glucuronide toxicity Anesthesiology 97 814-819, 2002... 

Suzuki S, Miyagi T, Chuang TK, Chuang LE, Doi RH, Chuang RY (2000) Morphine upregulates mu opioid receptors of human and monkey lymphocytes. Biochem Biophys Res Commun 279 621-628... 

Morphine and its derivatives continue to be considered the gold standard for alleviating pain. Morphine is metabolized in the liver via N-dealkylation and glu-coronidation at the third (M3G) or sixth position (M6G). Although M3G are the most common metabolites (accounts for 50% of the metabolites produced), they elicit no biological activity when bound to MOR. It is the M6G metabolite (accounts for 10% of the metabohtes produced) that elicits the nociceptive/analgesic effect upon binding to the p opioid receptor (Dahan et al. 2008). M6G is predominately eliminated via renal excretion. 

Heroin, a synthetic derivative of the p opioid receptor agonist morphine, is a well-documented narcotic that alters mood and rewarding behaviors. To date, heroin is the most abused opioid with an estimated 750,000-1,000,000 hardcore users in the... 

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