Autonomic Nervous System (ANS) Intro

Introduction to the Autonomic Nervous System (ANS)

• ANS regulates involuntary bodily functions.
• These include heart rate, blood pressure, digestion, and temperature control
• The two primary divisions of the ANS are the sympathetic (SNS) and parasympathetic (PNS) nervous systems.

Neurotransmitters of the ANS

• Acetylcholine (ACh) is the primary neurotransmitter in the PNS.
• ACh is used in the SNS for sweat glands and some blood vessels.
• Norepinephrine (NE) is the primary neurotransmitter in the SNS.
• Epinephrine (Epi) is released by the adrenal medulla and functions as a hormone.

Receptors in the ANS

• Cholinergic receptors are activated by Acetylcholine.
  • Nicotinic (N) receptors are at neuromuscular junctions, autonomic ganglia, and adrenal medulla.
  • Muscarinic (M) receptors are at effector organs of the PNS, like the heart, smooth muscle, and glands.
• Adrenergic receptors are activated by Norepinephrine and Epinephrine.
  • Alpha ($\alpha$) receptors include:
    • $\alpha_1$: Cause Vasoconstriction.
    • $\alpha_2$: Inhibit Norepinephrine release.
  • Beta ($\beta$) receptors include:
    • $\beta_1$: Increase heart rate and contractility.
    • $\beta_2$: Cause Bronchodilation and Vasodilation.
    • $\beta_3$: Cause Lipolysis.

Sympathetic Nervous System (SNS)

• The SNS mediates the "fight or flight" response.
• The SNS increases heart rate and blood pressure.
• It also causes pupil dilation and mobilizes energy stores.

Parasympathetic Nervous System (PNS)

• The PNS promotes the "rest and digest" response.
• The PNS decreases heart rate.
• It increases digestion and constricts pupils.

Cholinergic Drugs (affecting Acetylcholine)

• Cholinergic agonists (Parasympathomimetics):
  • Direct-acting agonists like Pilocarpine are used for glaucoma.
  • Indirect-acting agonists (Cholinesterase inhibitors):
    • Neostigmine treats myasthenia gravis.
    • Donepezil helps manage Alzheimer's disease.
• Cholinergic antagonists (Parasympatholytics):
  • Atropine increases heart rate and dilates pupils.
  • Scopolamine treats motion sickness
  • Ipratropium causes bronchodilation in COPD.

Adrenergic Drugs (affecting Norepinephrine and Epinephrine)

• Adrenergic agonists (Sympathomimetics):
  • $\alpha_1$ agonists like Phenylephrine are used as a decongestant.
  • $\alpha_2$ agonists like Clonidine are used for hypertension.
  • $\beta_1$ agonists like Dobutamine are used for heart failure.
  • $\beta_2$ agonists like Albuterol are used for asthma.
  • Mixed agonists like Epinephrine are used to treat anaphylaxis.
• Adrenergic antagonists (Sympatholytics):
  • $\alpha$ blockers like Prazosin are used for hypertension and BPH (Benign Prostatic Hyperplasia).
  • $\beta$ blockers like Propranolol are used for hypertension and anxiety.
    • Selective $\beta_1$ blockers like Metoprolol are used for hypertension.

Clinical Applications of ANS Pharmacology

• Hypertension is managed with $\beta$ blockers, $\alpha$ blockers, and $\alpha_2$ agonists.
• Asthma is managed with $\beta_2$ agonists and anticholinergics.
• Glaucoma is treated using cholinergic agonists and B blockers.
• Heart failure is treated with $\beta_1$ agonists short-term and B blockers long-term.
• Overactive bladder is treated using anticholinergics.

Noteworthy Drug Actions and Uses

• Atropine: A muscarinic antagonist used to increase heart rate and dilate pupils, with side effects like dry mouth and blurred vision.
• Albuterol: A $\beta_2$ agonist that causes bronchodilation for asthma, with side effects like tremors and tachycardia.
• Propranolol: A B blocker used for hypertension and anxiety, with side effects like bradycardia and fatigue.
• Pilocarpine: A muscarinic agonist used for glaucoma, which may cause increased salivation and diarrhea.
• Epinephrine: An $\alpha$ and $\beta$ agonist for anaphylaxis treatment, may cause tachycardia and anxiety.
• Neostigmine: A cholinesterase inhibitor used for myasthenia gravis, which may cause muscle weakness.
• Clonidine: An $\alpha_2$ agonist used for hypertension, which can cause sedation and dry mouth.
• Metoprolol: A selective $\beta_1$ blocker for hypertension, with possible side effects of bradycardia and fatigue.
• Prazosin: An $\alpha_1$ blocker is used for hypertension and BPH, can cause dizziness.
• Ipratropium: A muscarinic antagonist that treats COPD through bronchodilation, but it may have side effects that include dry mouth and blurred vision.
• Dobutamine: A $\beta_1$ agonist for short-term heart failure treatment, may cause arrhythmias.
• Phenylephrine: A $\alpha_1$ agonist for decongestion that may elevate blood pressure and cause headaches.
• Scopolamine: A muscarinic antagonist used for motion sickness, causes drowsiness.
• Donepezil: A cholinesterase inhibitor for Alzheimer's disease, that may cause nausea and vomiting.

Summary of Autonomic Drugs

• Cholinergic agonists stimulate muscarinic receptors.
  • These are primarily used for glaucoma and diagnosis of asthma.
  • They cause SLUDGE: salivation, lacrimation, urination, defecation, GI upset, and emesis.
• Cholinergic antagonists block muscarinic receptors.
  • They treat motion sickness and COPD and are used pre-anesthetically.
  • Common side effects include dry mouth, blurred vision, and constipation.
• Adrenergic agonists stimulate adrenergic receptors.
  • They treat asthma, hypotension, and nasal congestion
  • Cause hypertension, tachycardia, and anxiety.
• Adrenergic antagonists block adrenergic receptors.
  • They treat hypertension, BPH, and anxiety.
  • Risk hypotension, bradycardia, and fatigue.