Opioid Receptors and Mechanisms of Action

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is a common central nervous system effect associated with strong opioid agonists?

Increased gastrointestinal motility

Hypertension

Increased histamine release

Respiratory depression (correct)

Which cardiovascular effect can occur due to opioid agonism?

Bradycardia caused via CNS (correct)

Vasodilation and increased blood pressure

Tachycardia in all patients

Increased cardiac output

What gastrointestinal effect is commonly associated with the use of opioids?

Decreased motility leading to constipation (correct)

Enhanced appetite

Nausea with no vomiting

Increased risk of diarrhea

Which of the following is classified as a strong opioid agonist?

Fentanyl Signup and view all the answers

What happens to tolerance levels as opioid use continues over time?

Crosstolerance can occur but is not always complete Signup and view all the answers

Which type of opioid receptor is primarily associated with euphoria and has the highest effect from endorphins?

µ receptor Signup and view all the answers

What is a common physiological consequence of chronic opioid use?

Tolerance and dependence Signup and view all the answers

Which opioid receptor is most likely to induce dysphoria and has the strongest effect from dynorphins?

κ receptor Signup and view all the answers

What effect does opioid agonist activation primarily have on cardiovascular function?

Decreased respiratory rate Signup and view all the answers

Which mechanism is NOT commonly associated with the adaptations to opioid agonist activation?

Inhibition of K+ channels Signup and view all the answers

Which of the following best describes 'withdrawal' in the context of opioid dependence?

Physical and psychological symptoms caused by drug cessation Signup and view all the answers

Which statement about tolerance and dependence is accurate?

They lead to withdrawal symptoms when opioids are stopped. Signup and view all the answers

What effect do opioids have on gastrointestinal transit?

Decreased GI transit Signup and view all the answers

Which of the following accurately describes the central nervous system effects of µ agonists?

They produce both analgesia and respiratory depression, influenced by sensory input. Signup and view all the answers

What is the primary consequence of opioid-induced respiratory depression?

Diminished ability to respond to stimuli, especially in head trauma patients. Signup and view all the answers

Which of the following pain types tends to respond poorly to opioid treatment?

Neuropathic pain due to damage to neuronal structures. Signup and view all the answers

What factors influence the degree of respiratory depression caused by opioid agonists?

The degree of sensory input received by the body. Signup and view all the answers

Which class of opioids is primarily associated with the generation of euphoric sensations?

µ agonists that evoke pleasurable feelings. Signup and view all the answers

What is a common risk factor for developing opioid dependence?

History of addiction or ADHD in adolescents. Signup and view all the answers

What mechanism contributes to the experience of addiction after opioid withdrawal?

Persistent changes in brain reward pathways. Signup and view all the answers

What is the primary role of endogenous opioids during the fight or flight response?

To facilitate pain tolerance and enable quick reactions. Signup and view all the answers

Study Notes

Opioid Receptors and Their Effects

µ (Mu) receptors: Associated with euphoria, analgesia, decreased respiration, sedation, and reduced gastrointestinal transit. Tolerance and dependence can develop.
δ (Delta) receptors: Primarily linked to euphoria and analgesia. Develops tolerance but has less widespread effects compared to µ.
κ (Kappa) receptors: Induces dysphoria, sedation, and psychotomimetic effects with increased diuresis and decreased GI transit. Enkephalins activate these receptors strongly.

Mechanisms of Action

Opioid agonist activation leads to:
- Decreased adenylyl cyclase activity (post-synaptic inhibition)
- Increased K+ channel activity (post-synaptic inhibition)
- Decreased Ca+2 channel activity (pre-synaptic inhibition)
Adaptations from chronic opioid exposure result in tolerance, dependence, and withdrawal.

Definitions

Tolerance: Reduced drug efficacy with repeated use.
Dependence: Changes resulting in altered homeostatic balance leading to withdrawal syndrome.
Withdrawal: Physical and psychological symptoms from sudden drug cessation.
Addiction: Compulsive drug use characterized by an overwhelming focus on procurement and consumption.

Tolerance and Dependence Insights

Present in all patients; does not predict addiction or abuse risk.
Approximately 23% of individuals trying heroin may develop dependence, with 21-22% misuse rates.
Addiction occurs in a small percentage and typically follows prolonged exposure, marked by distinct epigenetic changes.

Non-CNS Effects of Opioids

Cardiovascular: May cause bradycardia and hypotension; meperidine can cause tachycardia due to antimuscarinic effects.
Gastrointestinal: Promotes constipation by reducing motility.
Renal: Leads to depressed function and antidiuresis.
Uterine effects: May prolong labor.
Pruritus: Histamine release can occur with parenteral administration.

Opioid Classification

Strong Opioid Agonists: Morphine, Hydromorphone, Oxymorphone, Heroin, Methadone, Meperidine, Fentanyl.
Weak Opioid Agonists: Codeine, Oxycodone, Hydrocodone, Diphenoxylate, Loperamide.

Tolerance Characteristics

High tolerance develops for analgesia, euphoria/dysphoria, sedation, and respiratory depression.
Moderate tolerance for cardiovascular bradycardia effects.
Little to no tolerance for miosis and constipation.
Crossover tolerance can occur but is usually incomplete, leading to variability when switching opioids.

Mechanism of Reward and Addiction

Activation of the mesolimbic dopamine pathway is linked to euphoria. This pathway connects the ventral tegmental area to the nucleus accumbens, influencing pleasure response.
Receptors for opioids, including κ and δ, are concentrated in the nucleus accumbens.

Analgesic Properties

Endogenous opioids enhance pain tolerance, crucial in protective mechanisms during stress.
Nociceptive pain responds well to opioids, while neuropathic pain may need higher doses or alternative treatments.

Results of Opioid Agonism

Central nervous system effects include sensory and emotional analgesia, euphoria, sedation, and respiratory depression.
Respiratory depression can occur even at therapeutic doses and is influenced by sensory input levels.

Therapeutic Uses

Opioids are used for moderate to severe pain relief, particularly in postoperative care and terminal illness, often combined with other agents for effective management.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on opioid receptors, their effects, and the mechanisms of action involved. This quiz covers the roles of µ, δ, and κ receptors, as well as concepts like tolerance and dependence. Perfect for students studying pharmacology or neuroscience.