VPT 321: Veterinary Neuropharmacology (2+1)

Non selective β-adrenergic receptor antagonists

NON SELECTIVE β - ADRENERGIC RECEPTOR ANTAGONIST

Propranolol

It interacts with both β₁ and β₂ receptors and blocks them competitively. It has powerful local anesthetic effect also.

• Cardiovascular effects
  • Blockade of β₁ –receptors produces decrease in heart rate, force of contraction and cardiac output. These are more evident during stress or exercise.
  • Cardiac work and oxygen demand are reduced. The AV conduction time is slowed, ectopic pacemaker activity is reduced and automaticity is suppressed.
  • Propranolol blocks cardiac stimulant action of adrenergic agonistic drugs, but not that of digitalis, Ca⁺⁺ or methylxanthines.
• Propranolol increases peripheral vascular resistance as a result of blockade of vascular β₂- receptors. Hence, blood flow to all organs, except heart decreases. Propranolol blocks vasodilatation and fall in blood pressure caused by adrenaline. Pressor response of noradrenaline is slightly reduced due to blockade of cardiac β₁response.
• Propranolol blocks β₂- adrenergic receptors in bronchial smooth muscle leading to increased airway resistance. This bronchoconstriction is more marked in asthmatic patients.
• Propranolol blocks adrenaline induced lipolysis and glycogenolysis.
• Clinically used as an anti arrhythmic drug.