Questions and Answers
What is the mechanism of action of beta blockers?
What is the primary effect of beta 1 receptor stimulation on the heart?
What is the effect of beta 2 receptor stimulation on blood vessels?
What is the effect of beta 1 receptor stimulation on the kidney?
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What is the effect of beta 2 receptor stimulation on the uterus?
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What is the advantage of selective beta 1 blockers over non-selective beta blockers?
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What is the effect of propranolol on the heart?
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What is the effect of beta 1 receptor stimulation on glycogen metabolism?
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What is the effect of beta 2 receptor stimulation on the skeletal muscles?
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What is the effect of β1 block on heart rate and force of contraction?
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What is the effect of β2 block on skeletal muscle blood vessels?
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What is the effect of β-blockers on oxygen requirement of the heart?
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Which of the following β-blockers has additional vasodilatory effect?
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What is the effect of β-blockers on renin secretion?
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Which of the following is a contraindication for β-blockers?
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What is the effect of β-blockers on cardiac output?
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Which of the following β-blockers has intrinsic sympathomimetic activity?
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What is the effect of β-blockers on aqueous humor formation?
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What is the effect of oxprenolol on heart rate in a patient with ischemic heart disease?
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What is the effect of β-blockers on bronchial airway resistance in patients with asthma and COPD?
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What is the effect of β-blockers on intraocular pressure in glaucomatous eye?
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What is the effect of β-blockers on glycogenolysis and glucagon secretion?
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What is the effect of β-blockers on recovery from hypoglycaemia in diabetics?
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What is the effect of β-blockers on HDL and LDL ratio?
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What is the effect of β-blockers on blood flow to skeletal muscles?
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What is the effect of β-blockers on anxiety symptoms?
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What is the effect of β-blockers with intrinsic sympathomimetic activity (ISA) on resting bradycardia?
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What is the result of up-regulation of β receptors?
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What is the clinical implication of up-regulation following abrupt withdrawal of β blockers?
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What is the mechanism of post-synaptic regulation?
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What is the result of down-regulation of β receptors?
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What is the clinical implication of down-regulation in bronchial asthma?
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What is the mechanism of pre-synaptic regulation?
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What is the effect of prolonged exposure to an antagonist on receptor number?
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What is the effect of prolonged exposure to β receptor agonists on receptor number?
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What is the reason for not stopping β blockers abruptly?
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What is the effect of β-blockers on thyrotoxicosis?
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What is the main use of esmolol?
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What is the main advantage of labetalol?
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What is the main advantage of carvedilol?
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What is the main difference between carvedilol and labetalol?
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What is the main advantage of nebivolol?
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What is a common adverse effect of β-blockers?
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What is a potential consequence of abrupt withdrawal of β-blockers after chronic use?
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What is the effect of β-blockers on lipid profile?
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Study Notes
Adrenergic Antagonists
- All β-blockers are competitive antagonists, blocking the β receptor mediated effects of sympathetic stimulation and adrenergic drugs.
- Non-selective β-blockers act at both β1 and β2 receptors, while cardio-selective or selective β-blockers block primarily β1 receptors.
- There is no absolute selectivity, and it depends on the dose.
β1 Adrenoceptors
- Distribution: postsynaptic – heart and juxtaglomerular apparatus in kidney
- Effect: excitatory
- Agonists: epinephrine, norepinephrine, dobutamine
- Antagonists: propranolol, atenolol
β2 Adrenoceptors
- Distribution: postsynaptic - lungs, uterus, skeletal muscle, blood vessels
- Effect: inhibitory
- Agonists: epinephrine, salbutamol
- Antagonists: propranolol
Effects of β Receptor Stimulation
- β1: tachycardia, increased myocardial contractility, increased release of renin, increased myocardial oxygen requirement
- β2: vasodilation, bronchodilation, uterine relaxation, glycogenolysis in muscle and liver
Effects of β Receptor Blockade
- β1: decrease heart rate and force of contraction, decrease in COP and BP, decrease oxygen requirement
- β2: slight constriction of skeletal muscle BV, increase in peripheral resistance, bronchospasm, decrease intraocular tension, delay recovery from hypoglycemia
Classification of β-Blockers
- Non-selective β-blockers: propranolol, timolol, pindolol, sotalol
- Cardio-selective (β1-selective) blockers: atenolol, bisoprolol, metoprolol, esmolol, acebutolol, celiprolol, betaxolol, nebivolol
- β-blockers with additional vasodilatory effect (α1-blocking action): labetalol, carvedilol
- β-blockers with intrinsic sympathomimetic (partial agonist) activity: pindolol, acebutolol, labetalol, celiprolol, and carteolol
- β-blockers with membrane stabilizing (local anaesthetic) activity: propranolol, acebutolol, carvedilol, labetalol, metoprolol, pindolol
Pharmacological Actions of Propranolol
- CVS: decrease in heart rate, conduction rate, force of contraction, cardiac output, and blood pressure
- Kidney: decrease in renin release, decrease in production of angiotensin II and aldosterone, decrease in BP
- Respiratory effects: blockade of β2 receptors, increase in bronchial airway resistance, bronchospasm in patients with asthma and COPD
- Eye: decrease in secretion of aqueous humour, decrease in intraocular pressure, local anaesthetic action
- Metabolic effects: inhibition of stress-induced glycogenolysis, decrease in glucagon secretion, delay recovery from hypoglycaemia, masking of warning signs and symptoms of hypoglycaemia
- Skeletal muscles: decrease in blood flow, skeletal muscle fatigue, inhibition of tremors
- CNS: decrease in anxiety symptoms, behavioral changes, forgetfulness, increased dreaming, nightmares
Therapeutic Uses of β-Blockers
- Esmolol: ultra-short acting selective β blocker, used I.V for rapid control of ventricular rate in supraventricular arrhythmias, and hypertensive emergencies
- Labetalol: competitive blocker at β1, β2 and α1 adrenergic receptors, used orally for hypertension and I.V for hypertensive emergency, safer to be used in pregnancy and pregnancy-induced hypertension
- Carvedilol: like labetalol, it blocks β1, β2 and α1 receptors, has antioxidant, antiproliferative, membrane stabilizing and vasodilatory properties, cardioprotective effect, and reduces mortality in patients with CHF
- Nebivolol: third-generation selective β1 blocker, has vasodilating activity, no membrane stabilizing and intrinsic sympathomimetic action, no unfavourable effects on lipid profile, used for control of hypertension and congestive cardiac failure
Adverse Effects of β-Blockers
- Bradycardia
- Coolness of hands and feet in winter
- CNS: mild sedation, vivid dreams, and rarely depression
- Alteration in lipid profile (increase in total TG, LDL, and decrease in HDL)
- Rebound hypertension, angina, MI can occur by abrupt withdrawal after chronic use
- Reduced exercise capacity
- GI upset, nightmares, forgetfulness, sexual distress
Regulation of Sympathetic Activity
- Pre-synaptic regulation: immediate, by α2 receptors
- Post-synaptic regulation: follows prolonged drug use, either increasing or decreasing the receptor number
- Up-regulation: increase in receptor number, leading to supersensitivity to the agonist when the antagonist is discontinued
- Clinical implication: following abrupt withdrawal of β-blockers, angina and myocardial infarction (ischemic heart disease) may be precipitated due to increased sympathetic activity.
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Description
This quiz covers the pharmacological actions of propranolol and beta blockers on various systems, their advantages, therapeutic uses, and contraindications.
