Posted by chemist on April 24, 2004, at 23:36:22
In reply to Re: MAOI causes hypotension - What's the mechanism?, posted by SLS on April 24, 2004, at 21:14:35
> OK. It looks like we were both wrong - at least according to what little I could find on the Net. I wish I could have found something more definitive, though. Maybe you'll have better luck.
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> I get the impression that the mechanisms by which MAOIs produce hypotension are poorly understood. One piece that I found stated that it definitely was not due to NE alpha-1 antagonism. The following is an excerpt from:
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> http://www.acnp.org/g4/GN401000046/CH046.html
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> SIDE EFFECTS OF MAOIS
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> Orthostatic Hypotension
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> Orthostatic hypotension is a common side effect of the irreversible MAOIs, particularly phenelzine (Table 4). Clinically, the development of orthostatic symptoms is gradual and appears generally after 2–3 weeks of treatment. The relationship of the time course of this response to the etiology of orthostasis remains unclear. Some have suggested it may represent a compensatory down-regulation of peripheral ganglionic effects in response to central sympathetic stimulation. Others have proposed that inhibition of amine metabolism results in an artificial, supraphysiologic elevation of amines with few or no pressor effects and the resultant replacement of amines with greater pressor effects from intracellular amine stores. Gradual accumulation of octopamine in adrenergic neurons, for instance, may be the result of MAO inhibition and resultant alternate hydroxylation of tyramine to octopamine. It has been suggested that octopamine may replace NE from intra-axonal storage granules. Octopamine released upon sympathetic stimulation may act as a 'false neurotransmitter' with minimal activity at a- or b-adrenergic receptors. The result is a functional block of sympathetic neurotransmission, accompanied by decreased ability to regulate blood pressure in response to postural changes.
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> - Scottchemist here....monoamineoxidase is an enzyme that is prevalent throughout your body. MAO inhibitors prevent the enzyme from oxidizing chemicals that contain an amino group ( to a nitroxide). this means that anything with a (ordinarily) oxizidable amino group does not get metabolized properly and the substance bulids up in your system. the dietary restrictions - and drug interactions - with MAOIs are most specific for sympathomimetic amines that cause central nervous system stimulation, such as amphetamine (dexedrine, adderall); provigil; methylphenidate; and other amino-rich substances. the interaction with ssris is that many of them block reuptake of norepinephrine, dopamine, and or course, serotonin. the trouble comes when you are on an MAOI and indulge in one of these substances. the equivalent is that of raising your blood pressure, becuase you have bumped-up the concentratioon of stimulants in yur system. this is why it is advisable to carry 50 mg thorazine with you in case you are slipped something like soy sauce in your meal. hypertension ensues, and this can lead to stoke or, at leasst, very uncomfortable hypertension.....all the best, chemist
poster:chemist
thread:339531
URL: http://www.dr-bob.org/babble/20040423/msgs/339716.html