Adrenergic Antagonists

• Adrenergic antagonists (also called adrenergic blockers or adrenolytics) are agents that bind to adrenergic (adrenaline/noradrenaline) receptors but do not activate them.
• By blocking these receptors, they inhibit the sympathetic (adrenergic) nervous system’s actions.

Classification of Adrenergic Antagonists

• They are broadly divided based on the types of adrenergic receptors they block:
  1. Alpha-adrenergic blockers (or α-blockers)
  2. Beta-adrenergic blockers (or β-blockers)
• Some agents can block both alpha and beta receptors (mixed blockers).

General Mechanisms of Action

• Prevention of receptor activation:

  • Adrenergic compete with endogenous catecholamines (e.g., norepinephrine, epinephrine) for receptor binding sites, preventing those endogenous substances from exerting their effect.

• Reduction in sympathetic tone:

  • By blocking alpha or beta receptors, these drugs reduce various sympathetic effects such as vasoconstriction, increased heart rate, and increased cardiac contractility.

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