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Questions and Answers
Which of the following drugs acts as a pure alpha agonist?
Which of the following drugs acts as a pure alpha agonist?
What effect do a1 agonists typically have on blood vessels?
What effect do a1 agonists typically have on blood vessels?
Which type of adrenergic agonist is primarily responsible for reducing sympathetic outflow and decreasing blood pressure when administered orally?
Which type of adrenergic agonist is primarily responsible for reducing sympathetic outflow and decreasing blood pressure when administered orally?
Which drug is classified as a b2 agonist that causes vasodilation?
Which drug is classified as a b2 agonist that causes vasodilation?
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What is a common side effect of administering a1 agonists due to their action on the vascular system?
What is a common side effect of administering a1 agonists due to their action on the vascular system?
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Which of the following is a legitimate use of amphetamine?
Which of the following is a legitimate use of amphetamine?
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What is a common adverse effect associated with high doses of amphetamine?
What is a common adverse effect associated with high doses of amphetamine?
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Which condition can be treated with central alpha-2 agonists?
Which condition can be treated with central alpha-2 agonists?
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What could result from the interaction between tyramine and MAO inhibitors?
What could result from the interaction between tyramine and MAO inhibitors?
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What is a potential effect of beta-2 agonists?
What is a potential effect of beta-2 agonists?
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At low doses, dopamine primarily activates which type of receptors?
At low doses, dopamine primarily activates which type of receptors?
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What effect do beta-2 agonists have on the respiratory system?
What effect do beta-2 agonists have on the respiratory system?
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Activation of alpha-1 receptors in the eye primarily causes what effect?
Activation of alpha-1 receptors in the eye primarily causes what effect?
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What is the effect of norepinephrine on heart rate when the reflex is not blocked?
What is the effect of norepinephrine on heart rate when the reflex is not blocked?
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The release of renin in the kidneys is stimulated by which type of receptor?
The release of renin in the kidneys is stimulated by which type of receptor?
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Which receptors are primarily responsible for the relaxation of the urinary bladder wall?
Which receptors are primarily responsible for the relaxation of the urinary bladder wall?
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What is the primary cardiovascular effect of pure alpha agonists?
What is the primary cardiovascular effect of pure alpha agonists?
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During pregnancy, which type of receptor causes the contraction of the uterus?
During pregnancy, which type of receptor causes the contraction of the uterus?
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What is the primary result of lipolysis in the body?
What is the primary result of lipolysis in the body?
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Which adrenergic agonist is best used to manage cardiogenic shock?
Which adrenergic agonist is best used to manage cardiogenic shock?
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What is the common CNS effect associated with high doses of catecholamines?
What is the common CNS effect associated with high doses of catecholamines?
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Which of the following is the drug of choice for anaphylactic shock?
Which of the following is the drug of choice for anaphylactic shock?
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Which adrenergic agonist is used to create mydriasis during an ophthalmologic exam?
Which adrenergic agonist is used to create mydriasis during an ophthalmologic exam?
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What condition is midodrine primarily used to treat?
What condition is midodrine primarily used to treat?
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What complication can arise from the use of beta2 agonists during premature labor?
What complication can arise from the use of beta2 agonists during premature labor?
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Which drug would be suitable for reducing congestion caused by irritation or allergy in the eyes?
Which drug would be suitable for reducing congestion caused by irritation or allergy in the eyes?
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Study Notes
Adrenergic Agonists
- Adrenergic agonists are drugs that mimic the effects of the sympathetic nervous system.
- They are categorized as general or selective agonists, based on their action on different adrenergic receptor subtypes.
- General agonists act on multiple receptor subtypes (α1, α2, β1, β2).
- Examples include Epinephrine, Ephedrine, Tyramine, Amphetamine, Cocaine, and Tricyclic antidepressants (TCAs).
- Selective agonists act primarily on one or a few receptor subtypes.
- Examples include Norepinephrine (α1, α2, β1), Phenylephrine (α1 > α2), Clonidine (α2 > α1), Isoproterenol (β1 = β2), Dobutamine (β1 > β2), Terbutaline (β2 > β1), Dopamine (acts on D1 receptors), and Bromocriptine (a dopamine agonist).
Vascular System Effects
- α1 agonists: Constrict blood vessels in skin, viscera, pulmonary, and renal regions. Leads to increased blood pressure (BP) and peripheral vascular resistance (PVR). Often cause bradycardia as a compensatory reaction.
- β2 agonists: Dilate arterioles in skeletal and coronary muscles; decrease PVR and BP. Can cause tremors in voluntary muscles.
- α2 agonists: When administered orally, they reduce sympathetic outflow from the central nervous system (CNS), thus decreasing BP. However, causes vasoconstriction when given intravenously or topically (e.g., nasal spray).
- Dopamine agonists: Act on D1 receptors in smooth muscles of renal, coronary, cerebral, and mesenteric arteries leading to relaxation. In the kidney, they inhibit Na+/K+ ATPase pump, promoting natriuresis (sodium excretion) and diuresis (fluid excretion).
Dopamine
- Low dose (0.5-2 mcg/kg/min): Activates dopamine receptors.
- Intermediate dose (2-10): Activates beta receptors.
- High dose (>10): Activates alpha receptors.
Cardiac Effects
- β agonists (e.g., isoproterenol): Primarily act on β1 receptors (and some β2) to increase heart rate, rate of cardiac pacemakers (normal and abnormal), force of contractions, and AV node conduction velocity.
Net Cardiovascular Actions
- α and β1 agonists (e.g., norepinephrine): Can cause reflex bradycardia due to increased blood pressure. The reflex often overrides any direct beta effects on heart rate.
- Pure alpha agonists (e.g., phenylephrine): Routinely slow heart rate through the baroreceptor reflex.
- Pure beta agonists (e.g., isoproterenol): Typically increase heart rate.
Respiratory System
- β2 agonists (e.g., terbutaline): Cause relaxation of tracheal and bronchial muscles.
Eye
- α1 agonists (e.g., phenylephrine): Cause contraction of radial muscles (pupillary dilator), resulting in mydriasis (pupil dilation).
- β2 agonists: Cause relaxation of ciliary muscles, important for far vision.
Gastrointestinal Tract
- α and β receptors: Found in smooth muscle and enteric neurons.
- Motility and tone: Affected by α2 and β2 receptors.
- Sphincters: α1 receptors cause sphincter contraction.
- Secretion: α2 receptors inhibit salt and water secretion in the intestine.
Genitourinary Tract
- Urinary bladder: β2 receptors relax the detrusor muscle, while α1 receptors constrict the trigones, sphincter, and prostate gland.
- Uterus: relaxes smooth muscles in non-pregnant tissue; in pregnant tissue, can cause contraction of α1 receptors and relaxation of β2 receptors.
Metabolic and Hormonal Effects
- Kidney: β1 receptors stimulate renin release.
- Pancreatic β cells: α2 receptors inhibit insulin release; β2 receptors stimulate insulin release.
- Glycogenolysis: β2 receptors stimulate glycogenolysis in liver and skeletal muscle.
- Glucose release from liver: Initially causes hyperkalemia; this leads to transfer of glucose to skeletal muscle, which can then result in hyperkalemia.
- Lipolysis: β3 receptors stimulate triglycerides (TGs) breakdown to fatty acids (FFAs), increasing lactate from lipid metabolism.
CNS Effects
- Catecholamines (like epinephrine and norepinephrine) themselves typically do not directly affect the CNS.
- Drugs like amphetamines have stimulant effects on the CNS, typically starting with mild alertness/fatigue reduction, then progressing to anorexia, euphoria, and insomnia. This effect is likely due to dopamine release in dopaminergic tracts. Higher doses can lead to anxiety, aggressiveness, paranoia, or seizures.
Cardiovascular Applications
- Increased blood flow: β1 agonists (e.g., dobutamine) increase blood flow in acute heart failure and cardiogenic shock. Dopamine is also useful, but primarily at higher doses.
- Reduced blood flow and increased BP: α agonists (e.g., norepinephrine) are used to increase BP in hypotension during surgery or anesthesia; α2 agonists (e.g., oxymetazoline) are used for congestion.
Respiratory Applications of Adrenergic Agonists
- Acute Asthma: β2 selective agonists (like terbutaline and albuterol) are the first choice for acute bronchoconstriction. Epinephrine and isoproterenol also work well.
- Emphysema/Bronchitis: These conditions may benefit from β2-agonists.
Other Applications
- Anaphylaxis: Epinephrine is a first-line treatment for anaphylactic shock (it acts on multiple adrenergic receptors; α1, β1, β2).
- Ophthalmic effects: α agonists, particularly phenylephrine, cause mydriasis, useful for eye examinations.
- Genitourinary applications: β2 agonists (ritodrine, terbutaline) are used in premature labor, although the cardiac stimulant effects warrant caution.
- CNS applications: Amphetamines are used for narcolepsy, ADHD, and weight loss.
Drug Interactions
- Tyramine and MAO inhibitors: Tyramine, found in many foods, is normally metabolized by MAO. MAO inhibitors increase tyramine's effect which elevates NE leading to hypertensive crisis.
Adverse Drug Reactions (ADRs) of Sympathomimetics
- Catecholamines: High doses can cause severe vasoconstriction, cardiac arrhythmias, myocardial infarction (MI), pulmonary edema, hemorrhage, and tissue necrosis.
- Amphetamines: Toxicity ranges from mild to severe, depending on the dose. Mild effects (nervousness, anorexia, insomnia) are possible at lower doses, while high doses can lead to anxiety, aggressiveness, paranoia, and seizures.
- Peripherally acting agents: α1 agonists (e.g., phenylephrine) can cause reflex hypertension and bradycardia. β1 agonists (e.g., isoproterenol) can cause palpitations, tachycardia, and serious arrhythmias. β2 agonists (e.g., terbutaline) can cause skeletal muscle tremors.
- Selectivity at high doses: All sympathomimetics lose their selectivity at high doses.
- Cocaine: High doses are linked to cardiac arrhythmias, heart attack, and seizures.
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Description
Test your knowledge on adrenergic agonists with this quiz covering their classifications, effects, and therapeutic uses. From alpha and beta agonists to the interactions of specific drugs, this quiz will challenge your understanding of pharmacological principles. Perfect for students and professionals in the field of pharmacology!
