Autocoid pharmacology: histamine, serotonin, kinins, prostaglandins and opioid autacoids MCQs With Answer

Introduction: Autacoids are locally acting chemical mediators that play crucial roles in inflammation, vascular tone, pain and homeostasis. This quiz set focuses on autocoid pharmacology — histamine, serotonin, kinins, prostaglandins and endogenous opioid autacoids — addressing receptor subtypes, signaling mechanisms, pharmacokinetics and therapeutic implications relevant to M.Pharm students. Questions emphasize receptor pharmacology, drug-receptor interactions, clinical use and adverse effects, and biochemical pathways including synthesis and degradation. These MCQs are designed to deepen understanding for advanced pharmacology, aiding exam preparation and encouraging critical thinking about drug design, selectivity and mechanism-based safety considerations.

Q1. What is the primary intracellular second messenger mechanism activated by H1 histamine receptor stimulation in vascular endothelial and smooth muscle cells?

• Activation of adenylate cyclase and increase in cAMP
• Inhibition of phospholipase C and decreased IP3
• Activation of phospholipase C with increased IP3 and DAG
• Activation of guanylate cyclase and increased cGMP

Correct Answer: Activation of phospholipase C with increased IP3 and DAG

Q2. Which histamine receptor subtype is primarily responsible for gastric acid secretion mediated via parietal cells?

• H1 receptor
• H2 receptor
• H3 receptor
• H4 receptor

Correct Answer: H2 receptor

Q3. A patient on ACE inhibitor therapy develops a dry cough due to accumulation of which autacoid?

• Serotonin
• Bradykinin
• Prostaglandin E2
• Substance P

Correct Answer: Bradykinin

Q4. Sumatriptan exerts its antimigraine effect primarily by agonism at which receptor subtype?

• 5-HT1B/1D receptors
• 5-HT2A receptors
• 5-HT3 receptors
• 5-HT4 receptors

Correct Answer: 5-HT1B/1D receptors

Q5. Which enzyme is the rate-limiting step in prostaglandin synthesis from arachidonic acid?

• Prostaglandin synthase (PGIS)
• Cyclooxygenase (COX) also called prostaglandin-endoperoxide synthase
• Lipoxygenase (5-LOX)
• Thromboxane synthase

Correct Answer: Cyclooxygenase (COX) also called prostaglandin-endoperoxide synthase

Q6. Which prostaglandin is a potent vasodilator and inhibitor of platelet aggregation, produced mainly by endothelial cells?

• Thromboxane A2 (TXA2)
• Prostaglandin F2α (PGF2α)
• Prostaglandin I2 (prostacyclin, PGI2)
• Prostaglandin D2 (PGD2)

Correct Answer: Prostaglandin I2 (prostacyclin, PGI2)

Q7. Which pharmacological property best explains COX-2 selective inhibitors’ reduced risk of gastrointestinal ulceration compared with nonselective NSAIDs?

• Preferential blockade of COX-1 in platelets
• Selective inhibition of inducible COX-2 while sparing constitutive COX-1 in gastric mucosa
• Stronger inhibition of lipoxygenase pathway
• Increased prostaglandin synthesis in gastric mucosa

Correct Answer: Selective inhibition of inducible COX-2 while sparing constitutive COX-1 in gastric mucosa

Q8. Bradykinin exerts most of its proinflammatory and pain-producing actions via which receptor subtype under physiological conditions?

• B1 receptor (inducible)
• B2 receptor (constitutive)
• NK1 receptor
• Kappa opioid receptor

Correct Answer: B2 receptor (constitutive)

Q9. Which statement about H3 histamine receptors is correct?

• H3 receptors are primarily postsynaptic excitatory receptors in smooth muscle
• H3 receptors function as autoreceptors regulating histamine release in the central nervous system
• H3 receptors mediate gastric acid secretion in parietal cells
• H3 receptors are important mediators of bronchoconstriction in asthma

Correct Answer: H3 receptors function as autoreceptors regulating histamine release in the central nervous system

Q10. Endogenous opioid peptides such as enkephalins produce analgesia mainly by activating which intracellular signaling pathway following opioid receptor binding?

• Gs protein–mediated increase in cAMP
• Gi/Go protein–mediated inhibition of adenylate cyclase and decreased cAMP
• Gq-mediated activation of phospholipase C
• Tyrosine kinase receptor activation

Correct Answer: Gi/Go protein–mediated inhibition of adenylate cyclase and decreased cAMP

Q11. A pharmacological antagonist that prevents histamine release from mast cells by stabilizing the mast cell membrane is:

• Ranitidine
• Cromolyn sodium
• Loratadine
• Diphenhydramine

Correct Answer: Cromolyn sodium

Q12. Which prostaglandin is primarily involved in uterine contraction and is used clinically for induction of labor or termination of pregnancy?

• Prostaglandin E2 (PGE2)
• Prostaglandin I2 (PGI2)
• Prostaglandin D2 (PGD2)
• Prostaglandin E1 (PGE1)

Correct Answer: Prostaglandin E2 (PGE2)

Q13. Which drug reduces serotonin reuptake and is commonly associated with serotonin syndrome when combined with MAO inhibitors?

• Sumatriptan
• Fluoxetine
• Ondansetron
• Metoclopramide

Correct Answer: Fluoxetine

Q14. Which kinin-degrading enzyme is directly inhibited by ACE inhibitors, contributing to elevated bradykinin levels?

• Kallikrein
• Aminopeptidase N
• Angiotensin-converting enzyme (ACE) itself degrades bradykinin
• Neutral endopeptidase (NEP) exclusively degrades bradykinin

Correct Answer: Angiotensin-converting enzyme (ACE) itself degrades bradykinin

Q15. Which of the following mediators is least likely to be categorized as an autacoid?

• Histamine
• Adrenaline released from sympathetic nerve endings
• Bradykinin
• Prostaglandins

Correct Answer: Adrenaline released from sympathetic nerve endings

Q16. Which adverse cardiovascular effect is most associated with selective COX-2 inhibitors due to imbalance between prostacyclin and thromboxane?

• Reduced platelet aggregation and bleeding tendency
• Increased risk of thrombosis and myocardial infarction
• Severe hypotension
• Bradycardia due to AV nodal blockade

Correct Answer: Increased risk of thrombosis and myocardial infarction

Q17. Which serotonin receptor is a ligand-gated ion channel and is important in chemotherapy-induced nausea and vomiting pharmacotherapy?

• 5-HT1A receptor
• 5-HT2A receptor
• 5-HT3 receptor
• 5-HT4 receptor

Correct Answer: 5-HT3 receptor

Q18. Which opioid receptor subtype is most closely linked to respiratory depression and euphoria produced by morphine-like agonists?

• Delta (δ) receptor
• Kappa (κ) receptor
• Mu (μ) receptor
• Nociceptin (ORL1) receptor

Correct Answer: Mu (μ) receptor

Q19. Which statement about prostaglandin E2 (PGE2) is correct in the context of inflammation?

• PGE2 causes vasoconstriction and reduces edema
• PGE2 sensitizes nociceptors and contributes to hyperalgesia
• PGE2 directly causes platelet aggregation
• PGE2 is only produced by platelets and has minimal inflammatory role

Correct Answer: PGE2 sensitizes nociceptors and contributes to hyperalgesia

Q20. Enkephalins are inactivated rapidly in the synaptic cleft primarily by which class of enzymes, making them unsuitable as therapeutic agents without modification?

• Monoamine oxidases
• Carboxylesterases
• Peptidases (enkephalinases) such as aminopeptidase N and neutral endopeptidase
• CYP450 enzymes

Correct Answer: Peptidases (enkephalinases) such as aminopeptidase N and neutral endopeptidase

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