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11 Cards in this Set
- Front
- Back
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Physiological Effects of Opiates
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Analgesia
Drowsiness Miosis (pupil constriction) Constipation Respiratory Depression |
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Evidence for Opiate Action at protein (receptor) site
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Stereoisomers- only the L isomer is active
Agonists can be turned into antagonists using simple structural changes |
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How do we know receptors mediate opiate effects?
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Labeled opiates- receptors found in CNS and peripheral tissue
Inhibition of gut contraction compared to peripheral binding in intestine - good correlation |
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Opiate Receptor Subtypes (type, action)
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All G-protein coupled:
mu: morphine affinity, analgesic, respiratory depression, reinforcement delta: reinforcement, motor/cognitive kappa: appetite, endocrine, and temp control |
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Mechanism of Opiate Action
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presynaptic inhibition of transmitter release:
Inhibition of Ca2+ influx increase in K+ permeability Inhibition of cAMP |
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Example of opiate pain blockade in the spinal cord
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example: enkephalin in spinal cord inhibits primary afferent substance P release onto neurons forming spinothalamic projections - pain blockade
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Method for identifying Endogenous Opiates
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1. competitive inhibition of labeled opiate antagonist
2. bioassay dependent on inhibition of transmitter release (smooth muscle contraction assay- opiates inhibit electrically stimulated contraction and effects are reversed by naloxone) |
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Steps in opiate peptide production and transport
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1. propeptides are produced in soma
2. stored in vesicles with converting enzymes 3. Transported along the axon in vesicles 4. Released, and degraded by proteases |
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3 Opiate Precursor Peptides
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Pro-opiomelanocortin - (endorphins)
Proenkephalin Prodynorphin |
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Link between cAMP and Opiate Tolerance and Withdrawal
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cAMP decreases acutely, upregulated with continued use. During withdrawal, cAMP spikes to abnormally high levels (decreased degradation or increased production)
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Drugs for opiate addiction cessation
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Methadone maintenance (or LAAM and buprenorphine with longer half lives)
Naltrexone and Nalmefene (antagonists) |
