Physiology

Catecholamines

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  • Synthesised from tyrosine in the presynaptic nerve terminal (via varies enzymatic steps)
  • Transported within vesicles to protect it from monoamine oxidases
    • MAO inactivate monoamines in cytoplasm
  • Exocytosis stimulated by calcium ion influx through channels that open in response to an action potential

  • Stimulates post-synaptic adrenoreceptors
  • Reabsorbed into the presynaptic neurone (uptake 1) or into surrounding tissues (uptake 2)
    • Uptake 1: inactivated by MAO or recycled into vesicles. MAO is active within neuronal synapses.

    • Uptake 2: inactivated by catechol-O-methyl transferase (COMT). COMT is active intracellularly

  • Adrenaline: vasodilatory effect via beta2-receptors, which exceeds its vasoconstriction effects elsewhere

  • Noradrenaline: vasoconstriction via alpha1-receptors so increases circulatory resistance and blood pressure

  • Half-life: 2 minutes

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