L-tyrosine, depression and smoking.

[phase_dancer]

thanks babydoc.
My concern stems from the fact that 5HTP is a direct precursor to serotonin and there is no rate limiting step, apart from perhaps vesicle limited 5HTP diffusion. Serotonin and its many receptors are distributed throughout the body, and because of the abundance of aromatic amino acid decarboxylase, wouldn't that mean 5HTP can be decaboxylated to serotonin anywhere cells have this enzyme (which is everywhere)?
What regulating mechanisms would be likely to prevent this? Could the excess be taken up by the pineal gland and converted to melatonin or would MAOA be able to handle such high amounts? If so, could this affect NE deamination?
I also wonder which would be the favoured excretory metabolite, and would these pathways be affected by other drugs, particularly alcohol which uses the same reductase and dehydrogenase as for 5-hydroxyindole aldehyde catabolism?

 

[fairnymph]

Although I'm not positive, I believe that your body would not absorb more 5-htp than necessary, and would also probably excrete excess 5-htp that it had already absorbed.
High doses of 5-htp are required for effective treatment of various mental health disorders because of the large distribution of serotonin throughtout the entire body. As a result of this distribution, only a small amount of any 5-htp that is taken reaches the brain. Thus, taking a higher dose increases the overall amount that crosses the blood brain barrier.
I believe that you can also boost the effectiveness of 5-htp in crossing the BBB by taking taking carpidopa concurrently. This lowers the dose of 5-htp needed.
Taking high doses of 5-htp certainly has bad side effects, and can be very expensive (by my estimates, ~US$600/month), and so other pharmacological treatments are usually preferable.
SMOKERS -- CHECK THIS OUT!
So, as you see above I mentioned that I predicted that reboxetine, the norepinephrine reuptake inhibitor, would be helpful for those trying to quit smoking. A recent study shows that reboxetine DOES indeed reduce nicotine cravings and administration (at least in rats).
[ 24 December 2002: Message edited by: fairnymph ]