I understand the kinetics and clearance and stuff, but I can’t wrap my head around how to tell what drug goes with what receptor and what it does when it gets there… What does it mean if something is described as muscarinic, nicotinic, adrenergic, or cholinergic? What is a catecholamine? Other than their physical location, is there any difference between alpha/beta/N/M receptors?
I’ve read books, looked at diagrams, watched videos, gone to lectures, and tried asking my profs but I still don’t understand and I’m going crazy because I always miss the pharm questions on my exams…
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Catecholamines are a handful of different molecules with a similar structure in the same pathway of synthesis (you make dopamine, which you can turn into norepinephrine, which you can turn into epinephrine.) We group them together because they’re closely related and have overlapping functions.
Think of the different receptors as different types of buttons you can push to send different messages. Each of them will have a different shape, which determines which molecules can push it. To your question, yes, alpha receptors are shaped different than beta receptors, and an alpha-1 receptor is shaped different than an alpha-2 receptor; this means that different catecholamines may prefer one to another. Alpha and beta receptors are also located in different places.
A cholinergic receptor binds acetylcholine. Muscarinic and nicotinic are two different types of cholinergic receptors that show up in different places. This is part of what gets confusing: Acetylcholine is one messenger chemical, but it can have very different effects at different places. Other chemicals can also affect this receptor, like nicotine at the nicotinic receptor or a bunch of drugs that block the muscarinic receptor.
An adrenergic receptor binds norepinephrine and epinephrine. Alpha and beta receptors are different types of adrenergic receptors. Likewise, they show up different places and thus have different effects.
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