Introduction: Understanding the distribution of adrenergic receptors is essential for B.Pharm students studying pharmacology, sympathetic nervous system responses, and drug action. This concise guide focuses on tissue-specific expression of alpha and beta receptors (alpha1, alpha2, beta1, beta2, beta3), receptor subtypes, and signaling pathways (Gs, Gi, Gq) that determine clinical effects of agonists and antagonists. Emphasis on vascular, cardiac, pulmonary, genitourinary, adipose and CNS distributions helps predict drug responses, side effects and therapeutic targets. Keywords: distribution of adrenergic receptors, alpha receptors, beta receptors, receptor subtypes, pharmacology, B.Pharm, MCQs with answers. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which adrenergic receptor subtype is primarily responsible for increased heart rate and contractility?
- Alpha1 receptor
- Alpha2 receptor
- Beta1 receptor
- Beta2 receptor
Correct Answer: Beta1 receptor
Q2. Activation of which receptor in bronchial smooth muscle causes bronchodilation?
- Alpha1 receptor
- Alpha2 receptor
- Beta1 receptor
- Beta2 receptor
Correct Answer: Beta2 receptor
Q3. Which receptor subtype is mainly located on presynaptic sympathetic nerve terminals and inhibits norepinephrine release?
- Alpha1 receptor
- Alpha2 receptor
- Beta1 receptor
- Beta3 receptor
Correct Answer: Alpha2 receptor
Q4. Stimulation of which receptor causes contraction of vascular smooth muscle and increases peripheral resistance?
- Beta2 receptor
- Alpha1 receptor
- Beta1 receptor
- Beta3 receptor
Correct Answer: Alpha1 receptor
Q5. Which adrenergic receptor subtype predominates in adipose tissue mediating lipolysis?
- Alpha1 receptor
- Alpha2 receptor
- Beta3 receptor
- Beta1 receptor
Correct Answer: Beta3 receptor
Q6. Which receptor couples to Gq protein and increases intracellular IP3 and DAG?
- Alpha1 receptor
- Alpha2 receptor
- Beta1 receptor
- Beta2 receptor
Correct Answer: Alpha1 receptor
Q7. Which receptor subtype in the kidney stimulates renin release when activated?
- Alpha1 receptor
- Alpha2 receptor
- Beta1 receptor
- Beta3 receptor
Correct Answer: Beta1 receptor
Q8. Epinephrine has relatively higher affinity for which receptor type at low concentrations leading to vasodilation in skeletal muscle?
- Alpha1 receptor
- Alpha2 receptor
- Beta2 receptor
- Beta1 receptor
Correct Answer: Beta2 receptor
Q9. Clonidine primarily acts on which adrenergic receptor to lower sympathetic outflow?
- Alpha1 receptor agonist
- Alpha2 receptor agonist
- Beta1 receptor agonist
- Beta2 receptor agonist
Correct Answer: Alpha2 receptor agonist
Q10. Which receptor subtype predominates in the urinary bladder detrusor and contributes to relaxation?
- Alpha1 receptor
- Beta2 receptor
- Beta3 receptor
- Alpha2 receptor
Correct Answer: Beta3 receptor
Q11. Non-selective beta blockers like propranolol block which receptor(s)?
- Only Beta1 receptors
- Only Beta2 receptors
- Both Beta1 and Beta2 receptors
- Alpha and Beta receptors equally
Correct Answer: Both Beta1 and Beta2 receptors
Q12. Which adrenergic receptor in the eye causes mydriasis when stimulated?
- Alpha2 receptor
- Beta1 receptor
- Alpha1 receptor
- Beta3 receptor
Correct Answer: Alpha1 receptor
Q13. Which receptor subtype is important for glycogenolysis in liver when activated by catecholamines?
- Alpha1 receptor
- Alpha2 receptor
- Beta2 receptor
- Beta3 receptor
Correct Answer: Beta2 receptor
Q14. Which adrenergic receptor subtype is coupled to Gi protein leading to decreased cAMP?
- Alpha1 receptor
- Alpha2 receptor
- Beta1 receptor
- Beta2 receptor
Correct Answer: Alpha2 receptor
Q15. Which adrenergic receptor subtype is most abundant in bronchiolar smooth muscle?
- Alpha1 receptor
- Beta1 receptor
- Beta2 receptor
- Beta3 receptor
Correct Answer: Beta2 receptor
Q16. Prazosin, an antihypertensive, primarily antagonizes which receptor?
- Beta1 receptor
- Alpha1 receptor
- Alpha2 receptor
- Beta2 receptor
Correct Answer: Alpha1 receptor
Q17. Which adrenergic receptor subtype is predominantly expressed in cardiac pacemaker cells?
- Alpha1 receptor
- Beta1 receptor
- Beta2 receptor
- Alpha2 receptor
Correct Answer: Beta1 receptor
Q18. Beta2 receptor activation in vascular smooth muscle causes relaxation via which second messenger?
- Increased IP3
- Increased DAG
- Increased cAMP
- Decreased cAMP
Correct Answer: Increased cAMP
Q19. Which receptor subtype in the gastrointestinal tract increases sphincter tone when stimulated?
- Alpha1 receptor
- Beta1 receptor
- Beta2 receptor
- Beta3 receptor
Correct Answer: Alpha1 receptor
Q20. Which adrenergic receptor subtype mediates thermogenesis in brown adipose tissue?
- Alpha1 receptor
- Beta1 receptor
- Beta2 receptor
- Beta3 receptor
Correct Answer: Beta3 receptor
Q21. The locus coeruleus in the CNS, involved in arousal and blood pressure regulation, is rich in which receptor?
- Alpha1 receptor
- Alpha2 receptor
- Beta1 receptor
- Beta2 receptor
Correct Answer: Alpha2 receptor
Q22. Which receptor subtype is primarily responsible for vasoconstriction of skin and splanchnic vessels?
- Beta2 receptor
- Beta1 receptor
- Alpha1 receptor
- Beta3 receptor
Correct Answer: Alpha1 receptor
Q23. Isoproterenol, a non-selective beta agonist, would most likely produce which cardiovascular effect?
- Marked vasoconstriction in skeletal muscle
- Increased heart rate and decreased peripheral resistance
- Decreased heart rate and increased blood pressure
- Increased renin release with bradycardia
Correct Answer: Increased heart rate and decreased peripheral resistance
Q24. Which receptor subtype is a common target for tocolytic drugs to relax the pregnant uterus?
- Alpha1 receptor
- Alpha2 receptor
- Beta1 receptor
- Beta2 receptor
Correct Answer: Beta2 receptor
Q25. Which receptor subtype in platelets modulates aggregation when activated?
- Alpha1 receptor
- Alpha2 receptor
- Beta1 receptor
- Beta3 receptor
Correct Answer: Alpha2 receptor
Q26. Chronic exposure to high agonist levels often causes downregulation via which mechanism?
- Increased receptor gene transcription
- Receptor internalization and degradation
- Enhanced receptor insertion into membrane
- Permanent receptor gene mutation
Correct Answer: Receptor internalization and degradation
Q27. Which adrenergic receptor subtype predominates in skeletal muscle vasculature mediating exercise hyperemia?
- Alpha1 receptor-mediated constriction only
- Beta2 receptor-mediated dilation and local metabolites
- Alpha2 receptor-mediated dilation
- Beta3 receptor-mediated constriction
Correct Answer: Beta2 receptor-mediated dilation and local metabolites
Q28. Selective beta1-blockers are preferred in patients with asthma because:
- They avoid bronchoconstriction mediated by beta2 blockade
- They strongly stimulate beta2 receptors
- They cause bronchodilation via alpha1 blockade
- They increase circulating epinephrine levels
Correct Answer: They avoid bronchoconstriction mediated by beta2 blockade
Q29. Which adrenergic receptor subtype in pancreatic beta cells modulates insulin release negatively?
- Beta2 receptor
- Alpha2 receptor
- Beta1 receptor
- Alpha1 receptor
Correct Answer: Alpha2 receptor
Q30. Which receptor subtype is most associated with skeletal muscle tremor when stimulated?
- Alpha1 receptor
- Beta2 receptor
- Alpha2 receptor
- Beta1 receptor
Correct Answer: Beta2 receptor
Q31. In coronary circulation, which adrenergic receptor contributes to vasodilation under sympathetic stimulation?
- Alpha1 receptor only
- Beta2 receptor
- Alpha2 receptor only
- Beta3 receptor
Correct Answer: Beta2 receptor
Q32. Which adrenergic receptor subtype is predominantly found in the prostate and mediates smooth muscle contraction?
- Alpha1A receptor subtype
- Beta1 receptor
- Beta2 receptor
- Alpha2B receptor subtype
Correct Answer: Alpha1A receptor subtype
Q33. Epinephrine’s vasoconstrictive effects at high doses are mainly mediated by which receptors?
- Beta2 receptors primarily
- Alpha1 receptors primarily
- Beta1 receptors primarily
- Alpha2 receptors primarily
Correct Answer: Alpha1 receptors primarily
Q34. Which receptor subtype mediates increased conduction velocity through the AV node?
- Alpha1 receptor
- Beta1 receptor
- Alpha2 receptor
- Beta3 receptor
Correct Answer: Beta1 receptor
Q35. Which adrenergic receptor subtype is primarily targeted by mirabegron for overactive bladder?
- Alpha1 receptor
- Beta1 receptor
- Beta2 receptor
- Beta3 receptor
Correct Answer: Beta3 receptor
Q36. Which receptor subtype contributes to decreased GI motility when activated by sympathetic stimulation?
- Beta2 receptor activation causing contraction
- Alpha1 receptor activation causing relaxation
- Alpha2 and beta2 receptor activation causing decreased motility
- Beta3 receptor activation increasing motility
Correct Answer: Alpha2 and beta2 receptor activation causing decreased motility
Q37. Which adrenergic receptor subtype is mainly responsible for ocular aqueous humor production increase?
- Alpha1 receptor
- Beta1 receptor
- Beta2 receptor
- Alpha2 receptor
Correct Answer: Beta2 receptor
Q38. Which pharmacological effect suggests predominant alpha1-mediated action of a sympathomimetic drug?
- Bronchodilation and tremor
- Increased heart rate without vasoconstriction
- Mydriasis and peripheral vasoconstriction
- Increased lipolysis only
Correct Answer: Mydriasis and peripheral vasoconstriction
Q39. Which adrenergic receptor subtype modulates thermogenic UCP1 expression in brown fat?
- Alpha1 receptor
- Beta1 receptor primarily
- Beta3 receptor primarily
- Alpha2 receptor
Correct Answer: Beta3 receptor primarily
Q40. An alpha2 agonist used for hypertension produces sedation by acting where?
- Peripheral vascular alpha2 receptors only
- Spinal alpha2 receptors only
- CNS alpha2 receptors such as locus coeruleus
- Beta receptors in the heart
Correct Answer: CNS alpha2 receptors such as locus coeruleus
Q41. Which receptor subtype is most implicated in reflex tachycardia following potent vasodilation?
- Alpha1 receptor activation
- Alpha2 receptor activation
- Baroreceptor‑mediated sympathetic activation of Beta1 receptors
- Beta3 receptor activation
Correct Answer: Baroreceptor‑mediated sympathetic activation of Beta1 receptors
Q42. Which adrenergic receptor subtype in the uterus leads to relaxation when stimulated near term?
- Alpha1 receptor
- Beta2 receptor
- Alpha2 receptor
- Beta1 receptor
Correct Answer: Beta2 receptor
Q43. Which subtype classification describes alpha2A, alpha2B and alpha2C receptors?
- They are beta receptor isoforms
- They are subtypes of alpha2 receptors with tissue-specific distribution
- They are muscarinic receptor subtypes
- They are unrelated enzyme isoforms
Correct Answer: They are subtypes of alpha2 receptors with tissue-specific distribution
Q44. Which drug effect indicates predominant beta1 blockade?
- Bronchospasm in asthmatic patient
- Decreased heart rate and contractility
- Marked uterine relaxation
- Increased lipolysis
Correct Answer: Decreased heart rate and contractility
Q45. Which adrenergic receptors are primarily responsible for mobilizing glucose by promoting glycogenolysis?
- Alpha1 receptors only
- Beta2 receptors in liver
- Alpha2 receptors in liver
- Beta3 receptors in liver
Correct Answer: Beta2 receptors in liver
Q46. Presynaptic alpha2 receptor activation has which immediate effect on synaptic transmission?
- Increases acetylcholine release
- Enhances norepinephrine release
- Decreases norepinephrine release
- Blocks dopamine synthesis
Correct Answer: Decreases norepinephrine release
Q47. Which statement best describes beta receptor distribution in the airway versus vasculature?
- Beta1 predominates in airways and beta2 in vasculature
- Beta2 predominates in airways and also mediates vasodilation in skeletal muscle vessels
- Alpha receptors only control both airway and vascular tone
- Beta3 receptors mediate major airway responses
Correct Answer: Beta2 predominates in airways and also mediates vasodilation in skeletal muscle vessels
Q48. In anaphylactic shock, epinephrine helps primarily by acting on which receptors?
- Alpha1 for vasoconstriction and Beta2 for bronchodilation
- Alpha2 only
- Beta3 only
- Muscarinic receptors primarily
Correct Answer: Alpha1 for vasoconstriction and Beta2 for bronchodilation
Q49. Which receptor subtype family includes alpha1A, alpha1B and alpha1D isoforms that show tissue-selective expression?
- Beta receptor family
- Alpha1 receptor family
- Muscarinic receptor family
- Histamine receptor family
Correct Answer: Alpha1 receptor family
Q50. Which phenomenon explains reduced responsiveness to a beta agonist after prolonged exposure?
- Receptor upregulation
- Receptor desensitization/downregulation mediated by GRKs and beta-arrestin
- Increased receptor gene expression
- Enhanced ligand synthesis
Correct Answer: Receptor desensitization/downregulation mediated by GRKs and beta-arrestin
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