Pharmacology Autonomic Nervous System Agents 3 — Questions and Answers
Question 1: A nurse administers epinephrine 1:1000 intramuscularly for anaphylaxis. At therapeutic doses, what is the PRIMARY cardiovascular effect?
- Increased heart rate and increased systolic blood pressure with decreased diastolic pressure (Correct answer)
- Decreased heart rate via vagal reflex only
- Selective vasoconstriction with no change in cardiac output
- Decreased myocardial contractility to reduce oxygen demand
Correct answer: Increased heart rate and increased systolic blood pressure with decreased diastolic pressure
Epinephrine increases heart rate and contractility (beta-1) and increases systolic BP while beta-2-mediated vasodilation in skeletal muscle decreases diastolic BP.
Question 2: Which of the following beta-blockers has intrinsic sympathomimetic activity (ISA) and is least likely to cause bradycardia at rest?
- Pindolol (Correct answer)
- Metoprolol
- Atenolol
- Propranolol
Correct answer: Pindolol
Pindolol has ISA, acting as a partial agonist at beta receptors, which maintains baseline heart rate while still blocking excessive sympathetic stimulation.
Question 3: Clonidine's antihypertensive effect is mediated by stimulation of which receptors in the CNS?
- Alpha-2 adrenergic receptors in the locus coeruleus and brainstem (Correct answer)
- Beta-1 receptors in the cardiac control center
- Muscarinic receptors in the hypothalamus
- Dopamine D2 receptors in the basal ganglia
Correct answer: Alpha-2 adrenergic receptors in the locus coeruleus and brainstem
Clonidine activates presynaptic alpha-2 receptors in the brainstem, reducing sympathetic outflow and lowering blood pressure.
Question 4: A patient with urinary retention post-operatively is given bethanechol. What is its mechanism of action?
- Direct muscarinic receptor agonist that stimulates detrusor muscle contraction (Correct answer)
- Acetylcholinesterase inhibitor increasing ACh at the neuromuscular junction
- Alpha-1 antagonist relaxing the urethral sphincter
- Beta-3 agonist increasing bladder capacity
Correct answer: Direct muscarinic receptor agonist that stimulates detrusor muscle contraction
Bethanechol directly activates muscarinic receptors on the detrusor muscle, promoting bladder contraction and urination.
Question 5: During a stress test, a patient is given isoproterenol. Which hemodynamic effect distinguishes it from epinephrine?
- Isoproterenol decreases diastolic blood pressure more than epinephrine due to pure beta-2 vasodilation (Correct answer)
- Isoproterenol causes greater alpha-1-mediated vasoconstriction
- Isoproterenol has no effect on heart rate
- Isoproterenol preferentially acts on alpha-2 receptors
Correct answer: Isoproterenol decreases diastolic blood pressure more than epinephrine due to pure beta-2 vasodilation
Isoproterenol is a pure beta agonist; its beta-2 vasodilation lowers diastolic BP without alpha-mediated vasoconstriction, unlike epinephrine.
Question 6: Timolol eye drops used for glaucoma can cause systemic bronchospasm because timolol is a:
- Non-selective beta-blocker that blocks pulmonary beta-2 receptors (Correct answer)
- Selective beta-1 blocker with partial agonist activity
- Alpha-1 antagonist reducing aqueous humor production
- Cholinesterase inhibitor increasing ciliary muscle tone
Correct answer: Non-selective beta-blocker that blocks pulmonary beta-2 receptors
Timolol is non-selective for beta receptors; systemic absorption through the nasolacrimal duct allows it to block bronchial beta-2 receptors causing bronchospasm.
Question 7: Which muscarinic receptor subtype primarily mediates bradycardia when the vagus nerve is stimulated at the sinoatrial node?
- M2 (Correct answer)
- M1
- M3
- M4
Correct answer: M2
M2 receptors in the SA node mediate vagal bradycardia by activating K+ channels (IKACh), hyperpolarizing the cell and slowing spontaneous depolarization.
Pharmacology Autonomic Nervous System Agents 3
A nurse administers epinephrine 1:1000 intramuscularly for anaphylaxis.
At therapeutic doses, what is the PRIMARY cardiovascular effect?