Uptake and Storage
Indirectly acting adrenergic agonists affect the uptake and storage mechanisms involved in adrenergic signalling.
Two uptake mechanisms exist for terminating the action of adrenergic catecholamines - uptake 1 and uptake 2. Uptake 1 occurs at the presynaptic nerve terminal to remove the neurotransmitter from the synapse. Uptake two occurs at postsynaptic and peripheral cells to prevent the neurotransmitter from diffusing laterally.
There is also enzymatic degradation of the catecholamines by two main enzymes - monoamine oxidase and catechol-o-methyl transferase. Respectively, these enzymes oxidise monoamines (including catecholamines) and methylate the hydroxal groups of the phenyl moiety of catecholamines. These enzymes can be targeted pharmacologically. Inhibitors of these enzymes act as indirect agonists of adrenergic receptors as they prolong the action of catecholamines at the receptors.
Read more about this topic: Adrenergic Agonist
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