Paradoxical dose-reponse curves

Matt Jones jonesmat at
Mon Sep 25 11:48:49 EST 1995

In article <Pine.SUN.3.91.950925104155.20184A-100000 at lucano> Depto.
Biologia Celular, bc2biced at writes:
>I need some information about the paradoxical dose-reponse curves. Do
>know any peptide which evokes this response? Please, send me references. 
>Thank you.

Can you please give more information about what is meant by
"paradoxical"? Many drugs can give "bell-shaped" curves, where the
response increases with dose at low concentrations, reaches a maximum,
and then decreases at high concentrations. Simple explanations for this
usually postulate two separate processes being induced by the same drug.
An example is the action of ACh a nicotinic receptors. At low to moderate
concentrations ACh activates channel opening, but at high concentrations
it appears to block the channel, reducing current. The bell shaped curve
probably results from the combination of a high affinity site of agonism,
and a low affinity site for block. 


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