Physiology
Catecholamines
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Get access- 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