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What is a common CNS effect of amphetamines?
Which characteristic differentiates ephedrine from other drugs in its category?
What potential psychological effect can occur with high doses of amphetamines?
What major cardiovascular effect can tricyclic antidepressants cause?
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What is a primary therapeutic use of beta blockers during an acute myocardial infarction?
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How does cocaine primarily enhance sympathetic transmission?
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Which drug may decrease the absorption of beta blockers?
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Which of the following is NOT a benefit of using beta blockers in patients with congestive heart failure?
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In the treatment of chronic open-angle glaucoma, which of the following beta blockers is used?
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Which statement is TRUE regarding the effects of beta blockers on pupil size when treating glaucoma?
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What types of effector cells are innervated by the autonomic nervous system?
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Which of the following correctly describes the function of the sympathetic nervous system?
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How many neurons are typically involved in the autonomic nervous system pathway from the CNS to effector organs?
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Which statement is true about the synaptic junctions in the autonomic nervous system?
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What is the primary function of the parasympathetic nervous system?
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What is the primary role of vesicular storage of norepinephrine (NE)?
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Which process contributes the most to the removal of norepinephrine from the synapse?
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What is the mechanism of β1-adrenoceptors primarily associated with?
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Which of the following accurately describes the comparative potency of a-AR and b-AR?
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Which subtype of adrenergic receptors is associated with bronchodilation?
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Which of the following describes a common effect of beta-adrenergic receptor antagonists on the cardiovascular system?
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Which medication is primarily used for the treatment of benign prostatic hyperplasia (BPH)?
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What is a notable side effect associated with the first doses of quinazolines?
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Which beta-adrenergic receptor antagonist is considered the prototype drug in its class?
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What characterizes b1-selective antagonists compared to non-selective antagonists?
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Which of the following effects occurs shortly after administering beta-adrenergic antagonists?
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What is the mechanism of action of Yohimbine?
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Which statement is true regarding intrinsic sympathomimetic activity (ISA) of certain beta-antagonists?
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Study Notes
Autonomic Nervous System
- Operates involuntarily on reflex control
- Maintains body's internal environment (homeostasis)
- Innervates smooth muscle, cardiac muscle, and exocrine glands
Somatic Nervous System
- Innervates skeletal muscle
- Voluntary control of skeletal muscle
Anatomical Differences: ANS vs SNS
- Two neurons in ANS, one neuron in somatic NS
- Synaptic junctions in ANS occur in ganglia, which lie outside the central nervous system. There are no such structures in the somatic NS.
- Efferent neurons in somatic NS are myelinated, while postsynaptic autonomic neurons are generally nonmyelinated.
Autonomic Nervous System Divisions
- Sympathetic nervous system (thoracolumbar)
- Parasympathetic nervous system (craniosacral)
- Enteric nervous system
Physiology of the ANS
- Controls smooth muscle, exocrine secretions, and heart rate and force
- Sympathetic and parasympathetic systems have opposing actions in some situations (e.g., heart rate control) but not in others (e.g., salivary gland function)
- Sympathetic activity increases in stress ('fight or flight'), while PNS activity predominates 'rest & digest'
- Both systems exert a continuous physiological control of specific organs under normal conditions
Vesicular Storage of NE
- Ensures regulated release of neurotransmitters
- Decreases intraneuronal metabolism
- Decreases leakage of NE to the extracellular sites
Release of NE
- Action potential triggers the exocytosis of NE-containing vesicles
- Similar process as release of Ach
- Neuropeptide Y and ATP are also released along with NE
Removal of NE From the Synapse
- Three processes contribute to termination of its transmitter role:
- Transport back into noradrenergic neuron (reuptake, uptake 1)
- Dilution by diffusion out of the junctional cleft and uptake into extraneuronal sites
- Metabolic transformation by MAO and COMT (catechol O-methyl transferase)
Adrenoceptors
- Can be broadly divided into two classes: α-AR and β-AR
- Comparative potency: - α-AR: EPI ≥ NE >>isoproterenol - β-AR: isoproterenol > EPI ≥ NE
- Α-AR: α1 and α2 subtypes
- α1A, α 1B, and α 1D
- α 2A, α 2B, and α 2C
- β-AR: β1 , β2 & β3 subtypes
- All are GPCR
β-AR
- Couple to Gs and activate adenylyl cyclase ( cAMP activation PKA activation of target proteins).
- β1 receptors are mainly found in the heart and have positive inotropic and chronotropic effects.
- β2 receptors mediate bronchodilatation, vasodilatation, and relaxation of visceral smooth muscle.
- Selective β2 agonists relax smooth muscle with minimal effect on the heart.
- Selective β1 antagonists have a useful blocking effect on the heart with minimal effect on bronchial smooth muscle.
- β3 receptors are involved in lipolysis.
Amphetamine: CNS Effects
- CNS effects are mediated by the release of biogenic amines from their storage sites in nerve terminals.
- Effects include alertness, anorexia, and locomotor stimulation.
- With higher doses, disturbances of perception and overt psychotic behavior occur.
Ephedrine
- Mixed-acting (causes release of biogenic amines from nerve terminals and also acts on both α- and β-AR)
- Has a longer duration of action (resistant to metabolism by MAO and COMT)
Other Drugs in This Category
- Methamphetamine
- Methylphenidate
- Pemoline
Drugs That Affect NE Uptake
- Tricyclic antidepressants (e.g., desipramine):
- Major effect is on the CNS but also cause tachycardia and cardiac dysrhythmias.
- Cocaine:
- Enhances sympathetic transmission, causing tachycardia and increased arterial pressure.
- Its central effects of euphoria and excitement are probably a manifestation of the same mechanism acting in the brain.
α1-AR Antagonists
- Efficacious in the treatment of BPH (benign prostatic hyperplasia) with little effect on blood pressure.
Adverse Effects
- First-dose effect: marked postural hypotension (quinazolines)
- Impaired ejaculation (tamsulosine)
Therapeutic Uses
- Treatment of hypertension (prazosin and congeners)
- Congestive heart failure
- Benign prostatic hyperplasia (especially tamsulosine)
Yohimbine
- Indolealkylamine alkaloid which is a selective competitive antagonist of α2-AR
- Readily enters the CNS and acts to increase BP and heart rate; it also enhances motor activity and produces tremors.
β-AR Antagonists
- Most are competitive antagonists of β-AR
- Useful in the treatment of hypertension, ischemic heart disease, CHF, and certain arrhythmias
- Propranolol: prototype drug in this group
β-AR Antagonist Subtypes
- Relative affinity for β1 and β2 receptors:
- Non-selective antagonists (propranolol, nadolol, timolol)
- β1-selective antagonists (metoprolol, atenolol, acebutolol, bisoprolol, and esmolol): selectivity is not absolute and is dose dependent.
- Intrinsic sympathomimetic activity (ISA):
- Pindolol and acebutolol: activate β-AR partially in the absence of catecholamines
- May be counterproductive to the response desired from a β-antagonist
- Prevent profound bradycardia or negative inotropy in a resting heart
- Differences in lipid solubility
- Pharmacokinetic properties
Pharmacological Effects
- CVS:
- Slow HR and decrease myocardial contractility
- cardiac output
- TPR
- Initial increase (blockade of vascular β2-AR and reflex stimulation of sympathetic activity)
- Returns to initial state or decreases with prolonged use
- in BP
CVS (cont’d)
- Reduce sinus rate, decrease the spontaneous rate of depolarization of ectopic pacemakers, slow conduction in the atria and in the AV node, and increase functional refractory period of the AV node.
Hypoglycemia and Bronchospasm
- Hypoglycemia is rare, and bronchospasm is uncommon in the absence of pulmonary disease.
Drug Interactions
- Aluminum salts, cholestyramine, and colestipol may decrease the absorption of β blockers.
- Phenytoin, rifampin, and phenobarbital, as well as smoking (inducers), may decrease plasma concentrations of β blockers.
Therapeutic Uses: Cardiovascular Diseases
- Myocardial infarction:
- Administered during the early phases of acute myocardial infarction and continued long-term may decrease mortality by about 25%.
- Precise mechanism is not known but may involve decreased myocardial oxygen demand, redistribution of myocardial blood flow, and antiarrhythmic actions.
Therapeutic Uses: Congestive Heart Failure
- Improve myocardial function, improve life quality, and prolong life.
- Reduce the mortality rate and reduce the hospitalization of patients.
Therapeutic Uses: Glaucoma
- Treatment of chronic open-angle glaucoma
- Carteolol, betaxolol, levobunolol, metipranolol, timolol, and levobetaxolol
- Have little or no effect on pupil size or accommodation and are devoid of blurred vision and night blindness.
Other Drugs That Block Adrenergic Transmission
- Guanethidine, guanadrel, bethanidine, debrisoquine
- Reserpine
- Ganglion blockers
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Description
Test your knowledge on the autonomic and somatic nervous systems with this quiz. Explore their functions, anatomical differences, and physiological roles in the human body. Perfect for students studying anatomy and physiology.
