Paper I
2017 August (Supplementary) (2010 Scheme) · 40 marks · 120 min

Question

Physiological antagonism.

Q63 marksShort Notes

Answer

Physiological (functional) antagonism occurs when two agonists act on different receptors or through different mechanisms to produce opposite effects on the same physiological function/organ system, without either drug directly blocking the other’s receptor.

Example

  • Histamine causes bronchoconstriction and hypotension (acting via H1 receptors), while adrenaline causes bronchodilatation and vasoconstriction/raised blood pressure (acting via β2 and α1 receptors respectively) — the two drugs physiologically oppose each other’s effects on the same organ systems despite acting through entirely different receptors

Clinical significance

  • This is the basis for using adrenaline in the emergency treatment of anaphylactic shock (where histamine is a major mediator) and bronchospasm

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