Pharmacology Lecture Notes: Adrenergic Antagonists

Introduction

• Sympathomimetics Review: Previous video discussed adrenergic agonists (sympathomimetics) that mimic the sympathetic nervous system.
• Current Focus: Adrenergic antagonists - drugs that block adrenergic receptors (alpha and beta receptors).

Adrenergic Receptors

• Types: Alpha receptors (Alpha 1, Alpha 2) and Beta receptors (Beta 1, Beta 2, Beta 3).
• Function:
  • Alpha 1: Increases smooth muscle contraction (vasoconstriction).
  • Alpha 2: Inhibits norepinephrine release (anti-sympathetic).
  • Beta (all types): Increase cyclic AMP (cAMP).

Adrenergic Antagonists (Sympatholytics)

• Types:
  • Alpha Blockers (Alpha antagonists)
  • Beta Blockers (Beta antagonists)
  • Alpha 2 Agonists: Anti-sympathetic, used to treat hypertension.

Blood Pressure Management

• Blood Pressure Formula: BP = Cardiac Output x Total Peripheral Resistance
• Alpha 2 Agonists: Decrease norepinephrine release, reducing heart rate and stroke volume.
• Alpha 1 Blockers: Cause vasodilation, reducing total peripheral resistance.
• Beta Blockers: Lower heart rate and stroke volume, reducing cardiac output.

Mechanism of Action

• Alpha Blockers: Block effects of noradrenaline, leading to vasodilation.
• Beta Blockers: Decrease heart rate and myocardial contractility.

Clinical Uses

• Hypertension: Alpha 2 agonists, Alpha 1 antagonists, Beta antagonists.
• Raynaud’s Disease: Alpha blockers improve blood flow.
• Benign Prostatic Hyperplasia (BPH): Alpha 1 blockers reduce urinary obstruction.

Side Effects

• Central Effects: Sedation, depression due to reduced norepinephrine.
• Peripheral Effects: Hypotension, reflex tachycardia.
• Retrograde Ejaculation: Due to Alpha 1 blockade.
• Metabolic Effects: Beta blockers may mask hypoglycemia symptoms.

Specific Drug Examples

• Centrally Acting Sympatholytics:

  • Reserpine: Decreases norepinephrine storage.
  • Clonidine, Methyldopa: Alpha 2 agonists reducing norepinephrine release.

• Peripherally Acting Alpha Blockers:

  • Non-selective: Phentolamine (reversible), Phenoxybenzamine (irreversible).
  • Alpha 1 selective: Prazosin, Doxazosin, Tamsulosin (less effect on BP).

• Beta Blockers:

  • Non-selective: Propranolol, Timolol.
  • Beta 1 selective: Atenolol, Metoprolol.
  • Combined Alpha/Beta Blockers: Labetalol, Carvedilol.

Specific Conditions

• Pheochromocytoma: Treated with non-selective alpha blockers first, then beta blockers.
• Pregnancy Hypertension: Methyldopa, Labetalol.
• Heart Failure: Avoid in acute conditions unless caused by tachycardia.

Additional Pharmacological Information

• Calcium Channel Blockers: Different class, but also treat hypertension by reducing heart contractility and vasodilation.

Educational Resources

• Online courses and resources available for further study on pharmacology.

This lecture provided detailed insights into adrenergic antagonists, their mechanisms, uses, and side effects within pharmacological treatments.