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Chapter 10: Opioids

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Mu (µ) opioid receptor activation leads to supraspinal analgesia via which of the following mechanisms?

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(A) decreased release of substance P from primary afferent inputs

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(B) increased release of dopamine in the nucleus accumbens

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(C) decreased activity in the ventrolateral medulla

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(D) decreased release of GABA from periaqueductal gray matter

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(E) decreased release of dopamine in the arcuate nucleus

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The answer is D. Mu (µ) opioid receptor activation at the spinal level decreases release of substance P from primary afferent inputs. Euphoria and mood-altering properties of opiates are mediated by increased release of dopamine in the nucleus accumbens. Respiratory rate and tidal volume are decreased by mu (µ) opioid receptor activation in the ventrolateral medulla. Prolactin release is increased by mu (µ) opioid receptor activation; this is due to presynaptically decreased release of dopamine in the arcuate nucleus.

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Refs: Brunton LL, Chabner BA, Knollman BC. Goodman & Gilman's the Pharmacological Basis of Therapeutics. 12th ed. New York, NY: McGraw Hill; 2011.

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Miller RD. Miller's Anesthesia. 8th ed. Philadelphia, PA: Elsevier; 2015.

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Activation of opioid receptors leads to activation of which intracellular transduction mechanism?

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(A) G proteins

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(B) adenylate cyclase

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(C) voltage gated calcium channels

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(D) voltage gated sodium channels

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(E) outward rectifying potassium channels

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The answer is A. G proteins (Gi and/or Go) are activated, as are inward rectifying potassium channels. Adenylate cyclase and voltage-gated calcium channels are inhibited by activation of the opioid receptor. Voltage-gated sodium channels are not involved in opioid receptor-activated intracellular transduction mechanisms.

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Refs: Brunton LL, Chabner BA, Knollman BC. Goodman & Gilman's the Pharmacological Basis of Therapeutics. 12th ed. New York, NY: McGraw Hill; 2011.

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Miller RD. Miller's Anesthesia. 8th ed. Philadelphia, PA: Elsevier; 2015.

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Which of the following opioids is the most hydrophilic?

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(A) morphine

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(B) fentanyl

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(C) codeine

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(D) methadone

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(E) heroin

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The answer is A. Morphine has a relatively low lipid solubility. Fentanyl, codeine, methadone, and heroin are all more lipophilic than morphine.

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Refs: Brunton ...

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