Opioid Receptor

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Opioid Receptors:

Opioid Receptors Presented b y- Akshat Bhargava M. Pharm (Pharmacology)

Introduction:

Introduction Opioid receptors are a group of G protein-coupled receptors with opioids as ligands . The endogenous opioids are dynorphins, enkephalins, endorphins and nociceptin. The opioid receptors are approx 40 % identical to somatostatin receptors (SSTRs). Opiate receptors are distributed widely in the - brain - spinal cord - digestive tract.

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Receptor Subtype Location Function delta ( δ) DOP OP 1 δ1, δ2 Brain, Peripheral Sensory nerves Analgesia, Antidepressant effects Convulsant effects kappa ( κ) KOP OP 2 κ1, κ2, κ3 Brain, Peripheral Sensory nerves , Spinal cord Analgesia, Anticonvulsant effects Neuroprotection, sedation mu ( μ) MOP OP 3 μ1, μ2, μ3 Brain, Peripheral Sensory nerves , Spinal cord, Intestinal tract μ1: Analgesia Physical dependence μ2: Respiratory depression Miosis Euphoria μ3: Possible vasodilation Nociceptin receptor NOP OP 4 ORL1 Brain , Spinal cord Anxiety, Depression, Appetite

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Peptides having morphine like action isolated from mammalian brain, pituitary, spinal cord and git. Active in very small amounts, their actions are blocked by naloxone, and they bind with high affinity to the opioid receptor. Three families of opioid peptides: Endorphins Enkephalins Dynorphins Derived from a large precursor polypeptide. ENDOGENOUS OPIOID PEPTIDES:-

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Endorphins :- β -endorphin has 31 amino acid derived from proopiomelanocortin . µ agonist , also has δ action. POMC – Anterior pituitary Pancreatic islet Enkephalins :- Pentapeptides - derived from peptide proenkephalin . Two type: met (ENK) equal affinity for µ and δ . leu (ENK) prefer δ receptor. D istribution in pain areas in - S pinal cord - A drenal medulla - G astric gland

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Dynorphins :- 8-17 amino acid peptides derived from prodynorphin. distribution parallel to proenkephalin. two type : DYN-A & DYN-B more potent for Ƙ but also act on µ & δ . Opioid peptide form a endogenous opioid system which generally modulates, - pain perception - mood - motor behavior - emesis - pituitary hormone release - git motility

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OPIOID RECEPTOR SUBTYPE & THEIR ENDOGENOUS PEPTIDES

Structure of Mu Opiate Receptor:

Structure of Mu Opiate Receptor

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Cellular Action or Transducer Mechanism OPIOID RECEPTOR ( G couple PROTEIN RECEPTOR) Inhibit adenylated cyclase Interacellular cAMP decreases Opening of K + channel Increase K + conductance Hyperpolarization Decrease exictability Inhibit opening of N type Ca 2+ channel Reduce availability of Ca 2+ channel Decrease transmittor release by CNS and myenteric neurons

μ- opioid receptor:-:

μ- opioid receptor:- The μ- opioid receptors (MOR) are a class of opioid receptors with high affinity : enkephalins and beta-endorphin low affinity : dynorphins They are also referred to as μ opioid peptide (MOP) receptors. The proto-typical μ receptor agonist is the opium alkaloid morphine. Effects:- Activation of the μ receptor by an agonist such as morphine causes analgesia , sedation, slightly reduced blood pressure, itching, nausea, euphoria, decreased respiration, miosis (constricted pupils) and decreased bowel motility often leading to constipation. Side E ffects : sedation , euphoria and decreased respiration, continuous use results in tolerance.

Deactivation:- :

Deactivation:- As with other G protein-coupled receptors, signaling by the MOR is terminated through several different mechanisms, which are up regulated with chronic use, leading to rapid tachyphylaxis. The most important regulatory proteins for the mu opioid receptor are the: β- arrestins : Arrestin β1 and Arrestin β2 , RGS proteins: RGS4, RGS9-2, RGS14 and RGSZ2. Long-term or high dose use of opioids may also lead to tolerance. This includes down-regulation of mu opioid receptor gene expression, so the number of receptors presented on the cell surface is actually reduced.

κ-opioid receptor :-:

κ-opioid receptor :- κ-opioid receptor ( KOR ) is a protein that in humans is encoded by the OPRK1 gene. It binds the opioid peptide dynorphin as the primary endogenous ligand (substrate naturally occurring in the body ). In addition to dynorphin , a variety of natural alkaloids and synthetic ligands bind to this receptor. Also provide a natural addiction control mechanism, and therefore, drugs that act as agonists and increase activation of this receptor may have therapeutic potential in the treatment of addiction.

Function :-:

Function :- κ-opioid receptor agonists are dysphoric but dysphoria from κ-opioid receptor agonists has been shown to differ between the sexes. Signal Transduction κ- Opioid receptor activation by agonists is coupled to the G protein G i /G 0 , which subsequently increases phosphodiesterase activity. Phosphodiesterase breaks down cAMP , producing an inhibitory effect in neurons.

Ligands :-:

Ligands :- Antagonists 5‘-Guanidinonaltrindole Norbinaltorphimine Amentoflavone Agonists Asimadoline Bremazocine BRL-52537 Pentazocine

δ-opioid receptor :-:

δ-opioid receptor :- The δ-opioid receptor , also known as delta opioid receptor or simply delta receptor , abbreviated DOR , is an opioid receptor that has enkephalins as its endogenous ligands. Activation of delta receptors produces some analgesia, although less than that of mu-opioid agonists. Many delta agonists may also cause seizures at high doses, although not all delta agonists produce this effect. Function :-

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Agonists Peptides Leu - enkephalin Met- enkephalin Deltorphins Non-peptides BU-48 SNC-80 BW373U86 DPI-287 DPI-3290 Antagonists Amentoflavone Naltriben Ligands :-

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