Adrenergic receptors are signal-receivers in the sympathetic nervous system. Broadly, there are alpha-1 -A, -B, and -D, alpha-2 -A, -B, and -C, and beta-1, beta-2, and beta-3 receptors. These do a bunch of different things which are beyond the scope of this note.
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Methylxanthine purine alkaloids in beverages.
Most of us talk about caffeine, and recently it has been hip to bring up theobromine in comparisons between chocolate and other beverages. The main pharmacodynamic of caffeine is to bind to alpha receptors.
Caffeine is metabolised into "12% theobromine, 4% theophylline, and 84% paraxanthine", all of which have adrenergic interactions.
Theobromine, as noted above, is famously found in chocolate, but also occurs naturally in some plants which are better known for their caffeine content.
Theophylline, also occurs naturally in similar places. By itself, it appears to be more aggressively adrenergic than caffeine, and it is shipped as a performance enhancing drug.
Paraxanthine is a metabolite of all of caffeine, theobromine, and theophylline. It is also adrenergic. It messes with nitric oxide signalling, and neurotransmitters such as glutamate and dopamine.
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Theacrine is found in some plants, being sometimes synthesised from caffeine. It is also binds to some alpha receptors. But it has attracted less interest and is deemed less effective than caffeine.
Many of the items above have histaminergic effects, which are beyond the scope of this note.
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For comparison, it has also been trendy ( thanks Hollywood ) to discuss beta-blockers a.k.a. beta-agonists. This is a related topic, but also beyond the scope of this brief note.
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