Adrenergic Drugs and Receptors Overview

Adrenergic Drugs

• Adrenergic drugs affect the sympathetic nervous system
• They play a crucial role in various physiological processes

Adrenergic Receptors: Location and Functions

• β₁: Located in the heart, increases heart rate, conductivity, and the force of contraction
• β₂: Located in bronchi, uterus, gastrointestinal tract (GIT), blood vessels (BV), and skeletal muscles; causes relaxation
• β₃: Located in adipose tissues, stimulates lipolysis
• α: Located in different organs; function varies depending on the specific alpha receptor subtype

Adrenergic Receptor Antagonists

• α-receptor antagonists: Nonselective, α₁-selective, α₂-selective
  • Nonselective: phenoxybenzamine, phentolamine
  • α₁-selective: prazosin, terazosin, doxazosin, alfuzosin, tamsulosin, urapidil, bunazosin
  • α₂-selective: yohimbine
• β-receptor antagonists: Nonselective, β₁-selective, β₂-selective
  • Nonselective: propranolol, nadolol
  • β₁-selective: atenolol, metoprolol, esmolol, acebutolol
  • Third-generation beta-blockers (β₁-selective): carvedilol, bisoprolol, nebivolol, labetalol

Beta-Blockers Classifications

• Nonselective: Block all β receptors (e.g., propranolol, nadolol)
• Selective β₁ (Cardio-selective): Block β₁ receptors (e.g., atenolol, metoprolol)
• Antagonists with partial agonist activity: Stimulate and block β receptors (e.g., pindolol, acebutolol)
• Antagonists of both α and β receptors (with VD activity): Block both α and β receptors with vasodilatory properties (e.g., labetalol, carvedilol)

Non-selective Beta-Blockers: Pharmacodynamics

• Heart (β₁): Negative inotropic, chronotropic, and dromotropic effects; decreases cardiac work and oxygen consumption, excitability, and automaticity
• Blood vessels (β₂): Reduction in vasodilation, unopposed α-mediated vasoconstriction
• Anti-hypertensive: Reduction in cardiac output (COP), sympathetic outflow from the central nervous system (CNS)

Non-Selective Beta-Blockers: Pharmacodynamics (Continued)

• Sodium (Na⁺) retention: Reduced blood pressure (BP) leads to reduced renal perfusion, increasing sodium retention and plasma volume
• Intraocular pressure (IOP): Reduction in aqueous humor synthesis
• Metabolism: Reduced glycogenolysis, lipolysis

Non-Selective Beta-Blockers: Pharmacodynamics (Continued)

• Central nervous system (CNS): Reduced anxiety, tremors (lipophilic beta-blockers)
• Local anesthetic action (some β-blockers): Sodium channel block, membrane stabilization, direct myocardial depression

Non-Selective Beta-Blockers: Therapeutic Uses

• Hypertension
• Angina: Decreases oxygen requirement of the heart muscle
• Myocardial infarction: Prevents further heart attacks
• Arrhythmias: Treats irregular heartbeats
• Glaucoma: Treatment of glaucoma
• Migraine headache
• Hyperthyroidism and Familial tremors

Non-Selective Beta-Blockers: Side Effects

• Bronchoconstriction: Potentially lethal in asthma and chronic obstructive pulmonary disease (COPD)
• Arrhythmias: Sudden withdrawal can worsen pre-existing conditions
• Sexual impairment: Impotence
• Hypoglycemia: Blocks manifestations and recovery in type 1 diabetes

β₁-Selective Blocker (Cardio-selective)

• Examples: Atenolol, acebutolol, metoprolol, esmolol
• Advantages: Less effect on pulmonary functions, peripheral resistance, and glucose homeostasis
• Disadvantages: Cardioselectivity can be lost at high doses

β₁-Selective Blocker (Cardio-selective) (Continued)

• Esmolol: Ultra-short-acting beta-blocker, destroyed by plasma esterase, administered intravenously
• Uses: Hypertension (with monitoring in asthma patients), diabetic hypertensive patients, acute or short-term hypertension and arrhythmias during procedures/emergencies

Antagonists with Partial Agonist Activity

• Examples: Pindolol, acebutolol
• Mechanism: Stimulate β receptors first, then block them
• Advantages: Less decrease in heart rate (HR) and cardiac output (CO), fewer disturbances in glucose and lipid metabolism

Antagonists of Both α and β Receptors

• Examples: Labetalol, carvedilol

• Mechanism: Produce vasodilation via α1 blockade, useful in hypertension with peripheral vascular resistance (PVD)

• Adverse effects: Orthostatic hypotension, dizziness

• β₁ Antagonists: Uses: Useful in elderly hypertensives, alternative to methyldopa in pregnancy-induced hypertension, rapid decrease in blood pressure (BP) in emergencies.

• β₁ Antagonists: Carvedilol's uses: Decreases lipid peroxidation and vessel wall thickening, useful in heart failure (HF)

Butaxamine

• Selective β₂ blocker, not used clinically

Drugs Affecting Neurotransmitter Release or Uptake

• Reserpine: Plant alkaloid; prevents storage of norepinephrine (NE), dopamine, and 5-hydroxytryptamine (5-HT) in vesicles; inhibits Mg²⁺/ATP-dependent transport; used to treat hypertension resistant to other drugs
• Guanethidine: Blocks release of NE; displaces NE from storage vesicles; causes orthostatic hypotension, male sexual dysfunction; can lead to hypertensive crises in patients with pheochromocytoma
• Cocaine: Local anesthetic; inhibits reuptake of both epinephrine and NE; increases the action of catecholamines

This quiz explores the functions and effects of adrenergic drugs on the sympathetic nervous system. It covers the locations and roles of various adrenergic receptors and details about receptor antagonists, including specific drugs and their classifications.