Chapters 15&16: Adrenergics and Cholinergics

AGONIST VS. ANTAGONIST

• Key Definitions:

  • Agonist: Activates a receptor leading to a physiological response.

  • Antagonist: Blocks a receptor, producing no physiological effect.

ANS - Autonomic Nervous System Terminology

• Muscarinic:

  • Describes the effects produced by acetylcholine on organ systems innervated by the parasympathetic system.

  • These receptors are selectively stimulated by muscarine.

• Nicotinic:

  • Refers to the effects of acetylcholine released in autonomic ganglia or neuromuscular junctions.

  • Nicotine selectively stimulates these receptors.

• Parasympathetic:

  • Relates to the effects of the parasympathetic nervous system (originating from cranial & sacral nerves).

• Adrenergic:

  • Relates to drugs or receptors mimicking the effects of norepinephrine or epinephrine.

• Sympathetic:

  • Refers to effects from nerve stimulation found in the thoracolumbar region of the spinal cord.

• Mimetic:

  • Mimics actions of a neurohormone (e.g., sympathomimetic drugs stimulate adrenergic receptors).

• Lytic:

  • Opposes the actions of a neurohormone (e.g., cholinolytic drugs antagonize cholinergic responses).

NERVOUS SYSTEM STRUCTURE

• Central Nervous System (CNS):

  • Comprised of the brain and spinal cord.

• Peripheral Nervous System (PNS):

  • Autonomic Nervous System (ANS): Regulates involuntary functions.

  • Sympathetic Division: Includes α-adrenergic and β-adrenergic receptors.

  • Parasympathetic Division: Includes muscarinic and nicotinic receptors.

  • Somatic Nervous System: Involved in voluntary control.

CLASSES OF AGONISTS AND BLOCKERS

• Adrenergic Agonists:

  • Epinephrine and Albuterol.

  • Central-Acting Alpha Agonists: Clonidine.

• Adrenergic Blockers:

  • Beta and Alpha Blockers.

• Cholinergic Agonists:

  • Bethanechol Chloride.

• Anticholinergics:

  • Atropine and Benztropine.

AUTONOMIC NERVOUS SYSTEM FUNCTIONS

• Regulate functions such as:

  • Heart rate

  • Respiratory rate

  • GI functions

  • Secretory glands

  • Smooth muscle control

CONFUSING NAMES CLARIFICATION

• Sympathetic Nervous System: Also known as the adrenergic system.

• Parasympathetic Nervous System: Known as the cholinergic system.

NEURON REVIEW

• Ion Channels:

  • Sodium (Na), Potassium (K), Calcium (Ca), Chloride (Cl).

• Action Potential: Electrical impulse along the neuron leading to neurotransmitter release.

RECEPTOR SPECIFICATION

• Autonomic Pathways:

  • Preganglionic neurons synapse with postganglionic neurons.

  • Autonomic fibers release neurotransmitters affecting target organs via receptors:

  • Adrenergic receptors for norepinephrine.

  • Muscarinic receptors for acetylcholine.

NEUROTRANSMITTER REVIEW

• Neurotransmitters: Chemicals allowing neuron signal transmission.

• Axon Terminals: Release neurotransmitters into the synaptic cleft.

• Neurotransmitter Fate:

  • Reuptake into the presynaptic neuron.

  • Enzymatic degradation.

  • Diffusion away from receptors.

EFFECTS OF DRUGS ON SYNAPTIC TRANSMISSION

• Interference with:

  • Transmitter synthesis, storage, and release.

  • Receptor binding leading to activation or inhibition.

  • Neurotransmitter reuptake and degradation processes.

SYMPATHETIC RECEPTORS

• Alpha1 Receptor Effects:

  • Vasoconstriction, mydriasis (pupil dilation), increased blood pressure, increased cardiac contractility.

• Alpha2 Receptor Effects:

  • Inhibit norepinephrine release, promote vasodilation, decrease blood pressure, reduce GI motility.

• Beta1 Receptor Effects:

  • Increase in heart rate and stroke volume, increased renin secretion, renal vasoconstriction.

• Beta2 Receptor Effects:

  • Bronchodilation, decreased gastrointestinal motility, relaxation of uterine smooth muscles, and increased glycogenolysis.

DOPAMINERGIC RECEPTORS

• Location: Renal, mesenteric, coronary, and cerebral arteries.

• Effects of Stimulation: Increased blood flow via vasodilation.

NOREPINEPHRINE INACTIVATION

• Inactivation occurs through:

  • Reuptake into the neuron.

  • Enzymatic degradation (MAO and COMT).

  • Diffusion from the site of action.

ADRENERGIC AGONISTS

• Epinephrine (Adrenalin):

  • Indications: Anaphylaxis, bronchospasms, cardiogenic shock.

  • Contraindications: Tachydysrhythmias, closed-angle glaucoma.

  • Side Effects: Agitation, hyperglycemia, tachycardia, and life-threatening cardiac dysrhythmias.

CLASSIFICATION OF SYMPATHOMIMETICS

• Direct-acting: Stimulate adrenergic receptors (e.g., epinephrine, norepinephrine).

• Indirect-acting: Stimulate norepinephrine release (e.g., amphetamine).

• Mixed-acting: Both stimulate receptors and norepinephrine release (e.g., ephedrine).

CLASSIFICATION OF CATECHOLAMINES

• Endogenous Catecholamines: Epinephrine, norepinephrine, dopamine.

• Synthetic Catecholamines: Isoproterenol, dobutamine.

• Non-catecholamines: Phenylephrine, metaproterenol, albuterol. Can be orally administered and cross the blood-brain barrier.

EPINEPHRINE USAGE

• Mode of Action: Inotropic effects, vasoconstrictor, bronchodilator.

• Onset and Peak: Rapid.

EPINEPHRINE ADVERSE EFFECTS

• Monitoring Requirements: Assess BP, HR, urine output, and report adverse effects like hypertension or palpitations.

• Nursing Considerations: Manage use with care in specific patient populations.

CENTRAL-ACTING ALPHA AGONISTS

• Clonidine (Catapres):

  • Indications: Hypertension.

• Side Effects: Dry mouth, sedation, bradycardia.

• Methyldopa: Central alpha agonist with similar actions.

CLINICAL JUDGMENT CONSIDERATIONS

• Important for monitoring vital signs and recognizing cues related to perfusion.

• Maintain communication of changes in patient status.

ADRenergic ANTAGONISTS

• Beta-Adrenergic Blockers:

  • Block adrenergic neurotransmitter effects at receptor sites. Can be selective or non-selective (preferred).

  • Side Effects: Orthostatic hypotension, dizziness, sexual dysfunction.

  • Examples: Metoprolol (selective), Propranolol (non-selective).

ALPHA ADRENERGIC ANTAGONISTS

• Action: Promote vasodilation and decrease blood pressure.

• Example: Doxazosin mesylate (Cardura).

CHOLINERGIC AGONISTS AND ANTAGONISTS

• Parasympathetic Nervous System: Acetylcholine acts on muscarinic and nicotinic receptors.

  • Cholinergic Agonists: Direct-acting (Bethanechol) and indirect-acting agents (break down acetylcholine).

  • Cholinergic Antagonists: Known as anticholinergics (block acetylcholine action).

ENZYMATIC TRANSMISSION AND DEGRADATION

• Acetylcholinesterase (AChE): Inactivates acetylcholine post-release, allowing reuptake for recycling.

BETHANECHOL CHLORIDE (URECHOLINE)

• Indications: Treatment of urinary retention.

  • Side Effects: Tachycardia, bronchospasm, gastrointestinal upset, sweating.

ANTICHOLINERGIC DRUGS

• Uses: Overactive bladder, bradycardia.

  • Side Effects: Dry mouth, urinary retention.

  • Examples: Scopolamine, atropine, benztropine.

ANTICHOLINERGIC TOXICITY

• Symptoms: Mydriasis, dry mucous membranes, altered mental status.

• Adverse Effects Management: Monitoring for effects like tachycardia, urinary retention.

DRUGS TO KNOW

• Key Drugs: Atenolol, Bethanechol, Epinephrine, Benztropine, Tolterodine, Doxazosin, Atropine.