The autonomic nervous system controls involuntary functions in our body. Drugs can affect this system, either boosting or blocking its effects. These drugs work by interacting with specific receptors, mimicking or inhibiting natural chemicals in our body.

Understanding how these drugs work is crucial for treating various conditions. Some drugs speed up our heart rate and increase blood pressure, while others do the opposite. It's like having a remote control for our body's automatic functions.

Drugs Affecting the Autonomic Nervous System

Drug classes in autonomic system

• Cholinergic drugs act on acetylcholine receptors
  • Acetylcholine receptor agonists mimic the effects of acetylcholine (bethanechol)
  • Acetylcholinesterase inhibitors prevent the breakdown of acetylcholine, increasing its concentration (neostigmine)
• Anticholinergic drugs block the effects of acetylcholine
  • Muscarinic receptor antagonists block the effects of acetylcholine on muscarinic receptors (atropine)
• Adrenergic drugs act on adrenergic receptors (alpha and beta)
  • Sympathomimetic drugs mimic or enhance the effects of the sympathetic nervous system
    • Direct-acting drugs directly stimulate adrenergic receptors (phenylephrine)
    • Indirect-acting drugs increase the release or prevent the reuptake of norepinephrine (amphetamine)
    • Mixed-acting drugs have both direct and indirect effects (ephedrine)
  • Sympatholytic drugs block or reduce the effects of the sympathetic nervous system
    • Alpha-adrenergic receptor antagonists block the effects of norepinephrine on alpha receptors (prazosin)
    • Beta-adrenergic receptor antagonists block the effects of norepinephrine on beta receptors (propranolol)

Cholinergic vs adrenergic compounds

• Cholinergic compounds act on acetylcholine receptors and produce parasympathetic effects
  • Decreased heart rate and contractility reduce cardiac output (acetylcholine)
  • Increased gastrointestinal motility and secretion promote digestion (bethanechol)
  • Constriction of pupils causes miosis (pilocarpine)
  • Increased bronchial secretion and constriction can lead to bronchoconstriction (methacholine)
• Adrenergic compounds act on adrenergic receptors and produce sympathetic effects
  • Increased heart rate and contractility increase cardiac output (norepinephrine)
  • Decreased gastrointestinal motility and secretion reduce digestion (epinephrine)
  • Dilation of pupils causes mydriasis (phenylephrine)
  • Bronchodilation improves airflow in the lungs (albuterol)
  • Increased blood pressure results from vasoconstriction and increased cardiac output (dopamine)

Sympathomimetic vs sympatholytic drugs

• Sympathomimetic drugs mimic or enhance the effects of the sympathetic nervous system
  • Stimulate adrenergic receptors directly or indirectly increasing heart rate, blood pressure, and causing bronchodilation (epinephrine, pseudoephedrine)
  • Used to treat conditions such as hypotension, bradycardia, and bronchospasm
• Sympatholytic drugs block or reduce the effects of the sympathetic nervous system by antagonizing adrenergic receptors
  • Alpha-adrenergic receptor antagonists decrease blood pressure by reducing peripheral resistance (phentolamine)
  • Beta-adrenergic receptor antagonists decrease heart rate, contractility and reduce blood pressure (atenolol)
  • Used to treat hypertension, tachycardia, and angina pectoris

Nicotine's impact on cardiovascular control

• Nicotine stimulates nicotinic acetylcholine receptors in the autonomic ganglia and adrenal medulla releasing catecholamines
• Acute effects of nicotine increase heart rate, blood pressure, cause vasoconstriction and increase cardiac output and oxygen demand
• Chronic effects of nicotine lead to desensitization of nicotinic receptors and increased risk of cardiovascular diseases
  • Atherosclerosis narrows and hardens arteries reducing blood flow
  • Coronary artery disease reduces blood flow to the heart muscle
  • Myocardial infarction occurs when blood flow to the heart is blocked causing damage to heart tissue
  • Stroke happens when blood flow to the brain is disrupted leading to brain damage
• Withdrawal effects of nicotine include decreased heart rate, blood pressure and increased parasympathetic nervous system activity

Neurotransmission in the Autonomic Nervous System

• Neurotransmitters are chemical messengers that transmit signals across synapses
• The autonomic nervous system uses primarily acetylcholine and norepinephrine as neurotransmitters
• Adrenergic receptors are targets for norepinephrine and epinephrine in the sympathetic nervous system
• Cholinesterase is an enzyme that breaks down acetylcholine, terminating its effects
• The blood-brain barrier limits the entry of many autonomic drugs into the central nervous system
• Autonomic reflexes are involuntary responses mediated by the autonomic nervous system, regulating various bodily functions