Mu receptor

Mahajan SD, Schwartz SA, Shanahan TC, Chawda RP, Nair MP (2002) Morphine regulates gene expression of alpha- and beta-chemokines and their receptors on astroglial cells via the opioid mu receptor. J Immunol 169 3589-3599... 

Morphine acts on the mu receptor, and so do most of the clinically used opioid drugs. The detailed structure of these receptors has been described and we now have a reasonable understanding of their relative roles in physiological functions and in different pain states. 

There is little new with regard to the mu receptor, the main target for opioid drugs. The receptor is remarkably similar in structure and function in all species studied so animal studies will be good predictors for clinical applications. Although there have been suggestions of subtypes of the receptor, the cloned mu receptors have all been identical. 

All clinically used opiates have the same pharmacology since they all act on the mu receptor with the exception of the kappa agonist, pentazocine. Opiates are used to relieve moderate to severe pain whatever the cause (accidents, post-operative pain, cancer, etc.) and are used pre-, intra- and post-operatively. The mu opiates differ only in potency and pharmacokinetics. Examples are ... 

Heroin (diacetylmorphine) a highly lipophilic drug but has very weak or no affinity for opiate receptors. It penetrates the brain rapidly whereupon it is metabolised to morphine which then binds to the mu receptor. 

There are now selective antagonists for all three opiate receptors (see Table 21.2) but with the exception of naloxone they are experimental tools for probing the functional roles of the opiate receptors. Naloxone is a potent competitive antagonist at all three receptors with highest affinity for the mu receptor. It will rapidly reverse all opiate... 

Are the analgesic effects of PCP due to its local anesthetic properties or actions at sigma or perhaps mu receptors ... 

Berman JM, Goodman M, Nguyen TM-D, Schiller PW. Cyclic and acyclic partial retro-inverso enkephalins mu receptor selective enzyme resistant analogs. Biochem Biophys Res Commun 1983 115 864-870. 

Rossi G, Pan YX, Cheng J, Pasternak GW. (1994). Blockade of morphine analgesia by an antisense oligodeoxynucleotide against the mu receptor. Life Sci. 54 375-79. 

These differences in the behavioural properties of the opioid receptor sub-types are of considerable interest because the clinical use of currently marketed opioid analgesic drugs is limited by their undesirable side-effects, which include respiratory depression, constipation and an abuse or dependence liability. These side-effects have been associated with mu receptor ac-... 

Both U-62066 (spiradoline) (10) and PD 117302 (12) are racemic mixtures of two enantiomers. The kappa opioid activity has been shown to reside in the (—) enantiomer, and in the case of U62066 the (-h) enantiomer is a weak mu receptor agonist [49, 50]. (See above for discussion on absolute stereochemistry.)... 

Opiate mu receptor OPRMl Agonism Analgesia, Sedation. Physical dependence. Bowel dysfunction. Respiratory depression. Modulation of cough reflex. 

The plant alkaloids mimic the endogenous peptides enkephalins and endorphins (Chapter 12), which meditate nociception and sleep. There are three types of widely distributed opiate receptors. Mu receptors are concentrated in neocortex, striatum, thalamus, hippocampus, amygdala and spinal cord, delta receptors in neocortex and amydala, and kappa receptors in striatum, amygdala and hypothalamus (Mansour et al., 1988). 

Opioid receptors are found in the dorsal horn as well as in other areas throughout the spinal cord and brain. Three major classes of opioid receptors exist mu receptors (/r), kappa receptors (k) and delta... 

Zadina JE et al. Endomorphins novel endogenous mu-opiate receptor agonists in regions of high mu-receptor density. Ann NY Acad Sci 1999 897 136-144. 

Analgesic, respiratory, depression as well as euphoria produced by morphine result mainly from action at mu receptors. Most of the currently available narcotic analgesics act primarily on the mu receptors. 

It is a strong kappa receptor agonist and mu receptor antagonist. Its agonistic property is approximately three to four times more than pentazocine and its antagonistic property is approximately 10 times more than pentazocine. It has less abuse liability in comparison to pentazocine. It is useful in postoperative pain, myocardial infarction and labour. 

It is a potent and long acting opioid with partial mu receptor agonist property. 25 times more potent than morphine. Effects are similar to morphine but constipation is less marked. It undergoes extensive presystemic elimination and therefore is... 

It is N-allyl analogue of oxymorphone, have a high affinity for mu receptor and lower affinity at delta and kappa sites. It selectively antagonizes the respiratory depression produced by opioids. After intravenous administration, it antagonizes all actions of morphine. It also blocks the actions of endogenous opioid peptides. 

Chen, Z.R., Irvine, R.J., Somogyi, A.A., Bochner, F. Mu receptor binding of some commonly used opioids and their metabolites. Life Sci. 1991, 48, 2165-2171. 

Mu receptors are almost always located proximally, on the presynaptic side of the synapse. The periaqueductal gray is the region containing the most mu receptors, but they are also found in the superficial dorsal hom of the spinal cord, the external plexiform layer of the olfactory bulb, the nucleus accumbens (an area deeply implicated in the process of addiction), in some parts of the cerebral cortex, and in some of the nuclei of the amygdala. Mu receptors avidly bind enkephalins and beta-endorphin, but they have a low affinity for dynorphins (primarily a kappa receptor agonist).6... 

Delta receptor activation also produces analgesia, but it can also cause seizures as well. Delta receptors normally bind to a class of endogenous ligands known as enkephalins, but unlike mu receptors, information about delta receptors is limited. Enkephalins are peptides that are produced by the pituitary gland. Several different enkephalins have been identified. [3-Enkephalin resembles opiates because when it binds to a delta receptor, it relieves pain.11... 

Hydrocodone is a semisynthetic opioid derived from codeine.18It is utilized as an analgesic and antitussive available for oral administration, often in combination with acetaminophen or ibuprofen. As a rule, potent analgesics containing a methoxyl group at position 3 (e.g., hydrocodone, K, = 19.8 nM) bind the mu receptor relatively weakly, but their O-demethylated metabolites (such as hydromorphone, Kt = 0.6 nM) bind more strangely. As with oxycodone, the possibility exists that some of their ability to relieve pain may actually derive from their active metabolites 48... 

Buprenorphine is derived from thebaine. It is a partial mu agonist with kappa antagonist activity. Buprenorphine has 25 to 50 times the potency of morphine. It is used to produce a longer-lasting analgesia than morphine. Effects of buprenorphine last longer because it is released more slowly from mu receptors than morphine. It is available as an injectable for intramuscular (IM) or intravenous administration in a 1-ml solution containing 0.3 mg buprenorphine (as buprenorphine HC1) for the relief of moderate to severe pain. It is also available to treat opioid dependence in the formulation of a tablet,51 alone or in combination with naloxone, in 2- or 8-mg... 

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