64 Questions
Which gene encodes the precursor peptide Proenkephalin?
ENKEPHALIN
Where are the enkephalin peptides widely distributed?
Brain, spinal cord, adrenal medulla, and gastrointestinal tract
What receptors do enkephalins bind with high affinity?
Delta and mu receptors
Which peptide has a limited distribution, with cell bodies in the intermediate lobe of pituitary and in hypothalamus, and axons projecting to amygdala, PAG, brainstem, and spinal cord?
Beta-endorphin
Which peptide is distributed throughout the brain and spinal cord and functions as neurotransmitters?
Dynorphin
Which peptide has high affinity for mu and delta receptors and is released in response to stress?
Beta-endorphin
Which opioid receptor is associated with diuresis and dysphoria?
Kappa
Which opioid receptor is associated with constipation and respiratory depression?
Mu
Which opioid receptor is associated with reward and emotion?
Delta
Which cellular mechanism is targeted by opioids to reduce neurotransmitter release?
Close a voltage-gated Ca+2 channel on presynaptic neurons
What is the effect of opioids on postsynaptic neurons?
Open K+ channels
How do opioids reduce the formation of cAMP?
Inhibit adenylyl cyclase activity
Which of the following is a peripheral effect of opioids?
Spasm of smooth muscle in the biliary tract
Which of the following is true about the tolerance to constipating effects of opioids?
Tolerance does not develop
Which receptor does morphine primarily act on?
Mu receptor
What is the major route of metabolism for morphine?
Glucuronidation in the liver
Which active metabolite of morphine has high affinity for mu opioid receptors?
Morphine-6-glucuronide
What is the main indication for morphine use?
Moderate to severe pain
Which route is used for the elimination of conjugated morphine?
Glomerular filtration
What condition contraindicates the use of opioids?
Paralytic ileus
Which opioid is used as an analgesic and an antitussive?
Hydrocodone
Which opioid is formulated with aspirin or acetaminophen?
Codeine
Which opioid is more potent than morphine?
Hydromorphone
Which opioid has no active metabolites?
Hydromorphone
Which opioid is a mu receptor agonist and also has antimuscarinic properties?
Meperidine
Which opioid is used for relief of mild to moderate pain in ambulatory persons?
Codeine
Which opioid is metabolized by the liver and some of it is converted to morphine and is excreted in the urine?
Codeine
Which opioid is more lipid soluble than morphine?
Heroin
Which opioid is used as an analgesic and an antitussive?
Hydrocodone
Which opioid has indications for severe pain?
Hydromorphone
Which opioid has little effect on the gastrointestinal system, pupil, and cough reflex?
Meperidine
Which opioid is 80-100 times more potent than morphine?
Fentanyl
Which opioids are considered high-efficacy analgesics?
Morphine and fentanyl
Which opioids are considered lower efficacy analgesics?
Codeine and dihydrocodeine
Which drug is an agonist at kappa receptors and a weak antagonist at mu receptors?
Pentazocine
Which drug is a kappa receptor agonist and a weak partial mu receptor agonist?
Butorphanol
Which drug is a partial mu receptor agonist with kappa receptor antagonist actions?
Buprenorphine
Which drug is a kappa receptor agonist and a mu receptor antagonist?
Nalbuphine
Which drug is metabolized by glucuronidation?
Pentazocine
Which drug can precipitate a withdrawal syndrome in a person physically dependent on opioids?
Pentazocine
Which drug has high abuse liability and can cause psychotomimetic effects, dysphoria, increased heart rate, and blood pressure at high doses?
Pentazocine
Which drug has low abuse liability and less respiratory depression compared to full agonists?
Butorphanol
Which drug can be used to reverse respiratory depression produced by other opioids while maintaining analgesia?
Nalbuphine
Which opioid has the highest affinity for mu receptors followed by kappa and delta receptors?
Opioid receptor antagonists
Which opioid is a weak mu receptor agonist and inhibits the re-uptake of 5-HT and norepinephrine?
Tramadol
Which opioid is more effective in neuropathic pain and hyperalgesia than others?
Tapentadol
Which drug is indicated for moderate to severe pain and the treatment of opioid use disorder?
Buprenorphine
Which opioid has analgesic actions that are only partially antagonized by naloxone?
Tramadol
Which opioid is contraindicated in patients with pre-existing seizure disorders?
Tapentadol
Which medication is indicated for the treatment of acute opioid toxicity?
Naloxone
Which medication is used for the treatment of opioid use disorder and alcohol use disorder?
Naltrexone
Which medication is a peripherally-acting mu receptor antagonist for the treatment of opioid-induced constipation or pruritus?
Methylnaltrexone
Which medication is a peripherally-acting mu receptor antagonist for bowel recovery post-surgery?
Alvimopan
What is the potential risk of combining CNS depressants with antipsychotics, sedative-hypnotics, alcohol, and other CNS depressants?
Increased respiratory depression and orthostatic hypotension
What effect does naloxone have in an opioid-dependent patient?
Precipitates withdrawal syndrome
Which of the following is NOT a physiological effect of naloxone?
All of the above
Which opioid receptor does naloxone primarily target?
Mu receptor
What is the main purpose of naloxone administration?
To reverse opioid overdose
Which of the following reactions can occur when meperidine is co-administered with MAO inhibitors?
Excitation and hypertension
Which opioids can have adverse reactions when co-administered with MAO inhibitors?
Tramadol and tapentadol
What is a potential adverse effect of opioids on the fetus during obstetric labor?
Neonatal opioid depression
What is a paradoxical effect that opioids can have on renal and biliary colic?
Increased pain
Which of the following is an adverse effect of opioids except for meperidine?
Miosis
Which medication is used to treat acute opioid toxicity?
Naloxone
Study Notes
Opioid Receptors and Peptides
- The precursor peptide Proenkephalin is encoded by the PENK gene.
- Enkephalin peptides are widely distributed throughout the brain and spinal cord.
Enkephalin Peptides
- Met-enkephalin is a peptide with a limited distribution, found in the intermediate lobe of the pituitary and hypothalamus, with axons projecting to the amygdala, PAG, brainstem, and spinal cord.
- Leu-enkephalin is distributed throughout the brain and spinal cord, functioning as a neurotransmitter.
Opioid Receptors
- Enkephalins bind to opioid receptors with high affinity, specifically mu and delta receptors.
- Mu receptors are associated with reward and emotion, and are also involved in constipation and respiratory depression.
- Delta receptors are associated with analgesia and mood elevation.
- Kappa receptors are associated with diuresis and dysphoria.
Cellular Mechanism of Opioids
- Opioids target the cellular mechanism of reducing neurotransmitter release by inhibiting the release of GABA and glutamate.
- Opioids have a hyperpolarizing effect on postsynaptic neurons, reducing the formation of cAMP.
Peripheral Effects of Opioids
- Opioids can cause constipation, respiratory depression, and diuresis.
- Tolerance to the constipating effects of opioids develops over time.
Morphine
- Morphine primarily acts on mu opioid receptors.
- Morphine is metabolized by the liver and conjugated with glucuronic acid, then excreted in the urine.
- The active metabolite of morphine, morphine-6-glucuronide, has high affinity for mu opioid receptors.
- Morphine is indicated for the relief of severe pain.
Other Opioids
- Codeine is an opioid used as an analgesic and an antitussive, and is often formulated with aspirin or acetaminophen.
- Hydrocodone is an opioid used for the relief of mild to moderate pain in ambulatory persons.
- Fentanyl is an opioid that is more lipid soluble than morphine and is used for the relief of severe pain.
- Sufentanil is an opioid that is 80-100 times more potent than morphine.
- Butorphanol is an opioid with agonist activity at kappa receptors and weak antagonist activity at mu receptors.
Opioid Agonists and Antagonists
- Naloxone is a mu receptor antagonist used to reverse respiratory depression produced by other opioids.
- Buprenorphine is a partial mu receptor agonist with kappa receptor antagonist actions.
- Pentazocine is a kappa receptor agonist and a weak partial mu receptor agonist.
Opioid Use Disorders and Treatment
- Naloxone is indicated for the treatment of acute opioid toxicity.
- Methadone is used for the treatment of opioid use disorder and alcohol use disorder.
- Alvimopan is a peripherally-acting mu receptor antagonist used for the treatment of opioid-induced constipation or pruritus.
- Naldemedine is a peripherally-acting mu receptor antagonist used for bowel recovery post-surgery.
Test your knowledge on endogenous opioid peptides and their functions with this quiz. Learn about the genes that encode these peptides and their distribution in the body. Discover how enkephalin acts as a neurotransmitter and the receptors it binds to.
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