VPT 311: General and Systemic Veterinary Pharmacology (2+1)

RECEPTOR MEDIATED DRUG ACTION

Most important type of drug action

• Receptor is a binding site within biological tissues for either endogenous or exogenous(!!!) substances
• Macromolecules situated on the surface of the cell or inside the cell
• Regulate critical functions like enzyme activity, permeability, structural features, etc

Evidence

• Many drugs show structural specificity minor substitution alters the effect.
• Stereospecificity of drugs d-propranolol less active than l-isomer, l-noradrenaline – more potent than d- noradrenaline
• antagonism between substances of closely related structures some chemical identity Langley (1878) proposed the term receptive substance
• This idea developed by Clark (1920) – propounded the Receptor occupation theory D + R DR E (effect)
• The postulates of the theory are:
  • Intensity of response α fraction of receptors occupied; maximal response when all receptors are occupied ‘all or none’ action of drug on each receptor – each receptor is either fully activated or not at alldrug and receptor have structurally ‘lock and key’ arrangement