Posted by undopaminergic on June 5, 2008, at 5:34:11
In reply to Re: Is emsam and beta blocker possible?, posted by Amigan on June 4, 2008, at 14:57:36
> I have also asked in here why MAOIs are causing hypotention a few weeks ago, but nobody gave me an answer...
>
> If i'm not mistaken, selective MAOIs (either MAO-A or MAO-B) doesn't tend to cause this side effect. Only non-selective MAOIs like Parnate and Nardil does.
> If i am correct on this, i can only SPECULATE that it is the excessive dopamine responsible...
>The mechanisms underlying MAOI-induced hypertension are not well understood.
Dopamine may contribute, and so may desensitation of vascular alpha1-adrenoceptors. Another possible cause is false neurotransmission by trace amines that are normally metabolised by MAO, and that accumulate after inhibition of the enzyme, possibly displacing noradrenaline (NA) from storage vesicles in sympathetic nerve terminals. False neurotransmission would result if these trace amines were to be released in place of NA, due to their lack of potency as agonists at postsynaptic alpha1-adrenoceptors. In other words, loss of noradrenergic, or sympathetic, tone due to false neurotransmission is one hypothetical cause of MAOI-induced hypotension. Another factor that might contribute is enhanced stimulation of alpha2-adrenoceptors in the CNS, as this also results in reduced sympathetic acitivity. It is also known that a high extent of MAO inhibition - above 80% - results in a pronounced reduction of the rate of neurotransmitter synthesis, and this may be another contributory factor, although it would be expected to reduce any hypotension that is dependent on dopamine.
poster:undopaminergic
thread:832758
URL: http://www.dr-bob.org/babble/20080528/msgs/833040.html