Posted by Larry Hoover on May 24, 2003, at 14:53:37
In reply to Re: 5-HTP information - Larry, posted by Caleb462 on May 24, 2003, at 14:08:03
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> http://www.thorne.com/altmedrev/fulltext/5htp3-4.html
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> "It easily crosses the blood-brain barrier"
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> It does??? Well, damn, now I'm confused. So 5-HTP CAN cross the BBB and CAN be an effective AD? I thought it was all just hype.
>
> That begs the question, if supplemented 5-HTP can cross the BBB, then could supplemented serotonin itself cross the BBB? It shouldn't be possible, but neither should 5-HTP's crossing, right?When I look at studies such as the following one, I'm left with two hypotheses: a) 5-HTP uptake into the brain is an active process, by some as yet unidentified transporter (which may not work as well in depressives); b) 5-HTP uptake is a passive process, but the blood-brain barrier has different characteristics in depressives than in healthy people (potentially reducing the ability of all manner of substances to access the brain compartment).
There is no doubt the stuff gets into the brain. And, there's no doubt it does so by a different process than tryptophan, as the presence of other amino acids in the blood has no effect of 5-HTP uptake. PET studies (not referenced here) have shown radiolabelled serotonin and 5-hydroxyindoleacetic acid (5-HIAA, the metabolite of serotonin after it is "broken down" by monoamine oxidase) are present in the brain after dosing by radiolabelled 5-HTP.
In any case, and going back to a question first posed by samplemethod, pyridoxine taken with 5-HTP increases serotonin formation (in monkeys).
Acta Psychiatr Scand 1991 Jun;83(6):449-55
Low brain uptake of L-[11C]5-hydroxytryptophan in major depression: a positron emission tomography study on patients and healthy volunteers.
Agren H, Reibring L, Hartvig P, Tedroff J, Bjurling P, Hornfeldt K, Andersson Y, Lundqvist H, Langstrom B.
Department of Psychiatry, University Hospital, Uppsala, Sweden.
The precursor of serotonin, L-5-hydroxytryptophan (L-5-HTP), was radiolabelled with 11C in the beta-position, yielding [beta-11C]serotonin after decarboxylation, allowing positron emission tomography studies of L-5-HTP uptake across the blood-brain barrier. We studied 8 healthy volunteers and 6 patients with histories of DSM-III major depression, 2 with repeated examinations after clinically successful treatment. We report a significantly lower uptake of [11C]5-HTP across the blood-brain barrier in depressed patients, irrespective of phase of illness. The findings emphasize that serotonin is involved in depressive pathophysiology and support earlier suggestions that the transport of 5-HTP across the blood-brain barrier is compromised in major depression.
poster:Larry Hoover
thread:227441
URL: http://www.dr-bob.org/babble/20030520/msgs/228881.html