Adrenaline and Epinephrine: Sources, Chemistry, and Kinetics

Adrenaline (Epinephrine)

Source and Chemistry

• Found in adrenal medulla (80% of secretions) and some CNS tracts
• Oxidized to toxic adrenochrome when exposed to air and light, so prepared in dark brown ampoules
• Unstable in alkaline medium, stored in acidic medium

Kinetics

• Not absorbed orally
• Routes of administration:
  • Subcutaneous (½ ml 1/1000 Solution): vasoconstriction slows absorption, safe and long duration
  • Inhalation (1/100 Solution): by nebulizer or atomizer in bronchial asthma
  • Eye drops (2% solution): in open angle glaucoma and Loewi's test
  • Intra-Cardiac: in cardiac resuscitation, impaired circulation
  • IM: rapid absorption and short duration, used in anaphylactic shock
• Distribution: does not pass blood-brain barrier
• Fate:
  • Reuptake: 80% by nerve endings and tissues
  • Metabolism: 18% by MAO and COMT
  • Excretion: 2% unchanged in urine

Dynamics

Mechanism of Action

• Stimulates all adrenergic receptors (α1, α2, β1, β2, and weak β3)

Pharmacological Effects

• Local effects:
  • Skin and mucous membrane (α1 receptor): vasoconstriction, decongestion, and haemostasis
  • Eye:
    • Produces vasoconstriction of conjunctival blood vessels
    • No mydriasis due to destruction by alkalinity of tears and vasoconstriction of blood vessels
    • Effects on aqueous humor dynamics:
      • α1: vasoconstriction of ciliary vessels reduces aqueous formation
      • β2: facilitates trabecular outflow, decreasing IOP

Adrenaline (Epinephrine)

Source and Chemistry

• Found in adrenal medulla (80% of secretions) and some CNS tracts
• Oxidized to toxic adrenochrome when exposed to air and light, so prepared in dark brown ampoules
• Unstable in alkaline medium, stored in acidic medium

Kinetics

• Not absorbed orally
• Routes of administration:
  • Subcutaneous (½ ml 1/1000 Solution): vasoconstriction slows absorption, safe and long duration
  • Inhalation (1/100 Solution): by nebulizer or atomizer in bronchial asthma
  • Eye drops (2% solution): in open angle glaucoma and Loewi's test
  • Intra-Cardiac: in cardiac resuscitation, impaired circulation
  • IM: rapid absorption and short duration, used in anaphylactic shock
• Distribution: does not pass blood-brain barrier
• Fate:
  • Reuptake: 80% by nerve endings and tissues
  • Metabolism: 18% by MAO and COMT
  • Excretion: 2% unchanged in urine

Dynamics

Mechanism of Action

• Stimulates all adrenergic receptors (α1, α2, β1, β2, and weak β3)

Pharmacological Effects

• Local effects:
  • Skin and mucous membrane (α1 receptor): vasoconstriction, decongestion, and haemostasis
  • Eye:
    • Produces vasoconstriction of conjunctival blood vessels
    • No mydriasis due to destruction by alkalinity of tears and vasoconstriction of blood vessels
    • Effects on aqueous humor dynamics:
      • α1: vasoconstriction of ciliary vessels reduces aqueous formation
      • β2: facilitates trabecular outflow, decreasing IOP

This quiz covers the source, chemistry, and kinetics of adrenaline (epinephrine), including its presence in the adrenal medulla, chemical properties, and routes of administration. Learn about the absorption, preparation, and storage of adrenaline.