Mechanism of Action
Ephedrine is a sympathomimetic amine. The principal mechanism of its action relies on its indirect stimulation of the adrenergic receptor system, which is part of the sympathetic nervous system (SNS), by increasing the activity of noradrenaline at the post-synaptic α- and β-receptors. The presence of direct interactions with α-receptors is unlikely, but still controversial. L-Ephedrine, and particularly its stereoisomer norpseudoephedrine (which is also present in Catha edulis) has indirect sympathomimetic effects and due to its ability to cross the blood brain barrier, it is a CNS stimulant similar to amphetamines but less pronounced, as it releases noradrenaline and dopamine in the substantia nigra.
The presence of an N-methyl group decreases binding affinities at α-receptors, compared with norephedrine. On the other hand ephedrine binds better than N-methylephedrine, which has an additional methyl group at the N-atom. Also the steric orientation of the hydroxyl group is important for receptor binding and functional activity.
- Compounds with decreasing α-receptor affinity
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Norephedrine -
Ephedrine -
N-Methylephedrine
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