Introduction: General Principles-Lecture I, slide 1
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Aspects of Drugs
Anesthetic agents administered as racemic mixtures
Interactions: Binding Forces
The shape of the drug is an important
factor in defining the nature of the drug-receptor
interaction. The three-dimensional shape of the drug
is thought to interact with a complementary structural
binding region of the receptor, typically a protein.
The specific nature of the interaction defines whether the
drug acts as an agonist promoting a change in cellular
function or as an antagonist which blocks the receptor
usually resulting in no direct biological effect.
For example, let's consider
acetylcholine or a synthetic analogue bethanechol (Urecholine).
Interaction of these molecules with receptor
(nicotinic or muscarinic cholinergic receptor) causes
a physiological response, for example, a decrease in heartbreak
By contrast, a muscarinic
antagonist such as atropine may bind even more tightly
than acetylcholine to muscarinic receptor but causes
no direct effect.
administration of antagonist a biological response may
be observed as a result of receptor
A clinical example would be
bradycardia following acute myocardial
Bradycardia in this context
might be due to excessive parasympathetic (cholinergic)
tone and might cause unacceptably low cardiac
output or predispose to more serious
Administration of atropine, by
blocking the muscarinic receptor blunts the action
of acetylcholine and accordingly may reverse
Now let's consider the specific
example, acetylcholine, as the 2D planar structure:
On the left side of the molecule note
the quaternary (always positively charged) nitrogen, which is part
of the choline component of acetylcholine.
synthesis of acetylcholine proceeds by combination of choline and
acetate (as Acetyl-CoA)-see below