VPT 321: Veterinary Neuropharmacology (2+1)

Selective β- adrenergic receptor antagonists

SELECTIVE β - ADRENERGIC RECEPTOR ANTAGONIST

Selective β₁ – receptor antagonists

• Metoprolol is the prototype of cardioselective β₁- receptor blockers. Its potency to block β₁- receptors equals that of propranolol, but about 50-100 times higher dose is required to block β₂-receptors.
• Cardiovascular effects secondary to metoprolol’s negative inotropic and chronotropic actions include decreased sinus heart rate, slow AV conduction, decreased cardiac output, myocardial oxygen demand and reduced blood pressure. It reduces plasma renin activity in hypertensive patients. Unlike propranolol, metaprolol as relatively little effect on pulmonary function, peripheral resistance and carbohydrate metabolism.
• Clinical uses: It is used in arrhythmias, systemic hypertension, ventricular hypertrophy.
• Atenolol
  • Unlike propranolol and metoprolol, atenolol has very low lipid solubility, so it penetrates the brain only to a very limited extent.
• Esmolol
  • It is an ultra short acting β₁-rceptor blocker. It is given IV when β₁- receptor blockade is required for short duration. It is very useful for the investigation and immediate therapy of tachycardia.

Selective β₂-adrenergic receptor antagonists

• Butoxamine
  • It is relatively β₂-adrenergic receptor antagonist.
  • It is not used clinically as blockade of β2- adrenergic receptors has no therapeutic applications and on the other hand causes bronchoconstriction.