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Johnson, Samuel: "A man of genius has been seldom ruined but by himself."

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Caffeine Effects

Caffeine has four identifiable actions in vitro, but the relationship between these actions and the drugs effects in vivo are not well established.

In ascending order of dose response (i.e. from most sensitive to least sensitive) these are: 1. Adenosine receptor blockade, as you have already mentioned 2. Phosphodiesterase inhibition - this enzyme is responsible for the breakdown of cAMP and therefore this action of the methylxanthines leads to increased cAMP 2nd messenger functions. 3. Action at Ca++ channels to increase entry of Ca++ into cells and to decrease sarcolemma sequestration of Ca++. This may be related to the weak positive inotropic effect of the se drug at high dose rates (together with increased cAMP dep protein kinase activity due to number 2?) 4. Binding to GABA receptors at the benzodiazepine site (query clinical relevance because of high KD).