Posted by Scott L. Schofield on April 27, 2000, at 7:57:46
In reply to Re: More Qs for PeterJ, posted by PeterJ on April 27, 2000, at 0:33:49
Hi Andrew.
Peter's something, isn't he?
A few notes:
> > 2) Can tyrosine supplementation potentiate the effect of amineptine. One person stated that tyrosine potentiated dexadrine by preventing dopamine depletion. Amphetamines like dexadrine are D2 reuptake blockers. Amineptine has similar mechanics, being a dopamine reuptake blocker.
> I would expect tyrosine to have some potentiating effect. In animal studies, tyrosine conversion to dopamine is increased in situations of increased dopamine turnover. In human studies, delpletion of serum tyrosine has been shown to prevent the stimulant effects of amphetamine. Thus tyrosine might reduce any dopamine depletion by amineptine. The magnitude of this effect and whether or not it would prevent withdrawal symptoms is harder to estimate. Tyrosine does seem to have modest clinical benefits in some cases of depression or stimulant addiction.
To give tyrosine a good shot at doing anything in the brain, it needs to get there in the first place. Tyrosine competes with other amino acids for uptake across the blood-brain barrier. It competes with other large neutral amino acids for access to L-system carrier uptake sites. These other amino acids comprise tryptophan, phenylalanine, leucine, isoleucine, and valine. It is suggested that any of these should be ingested in the absence of all the others. Tyrosine should therefore be taken on an empty stomach or along with a meal devoid of protein. Phenylalanine may be a better choice to fill the role proposed for tyrosine "supplementation" in treating depression. It tends to cross the blood-brain barrier more easily. Once in the brain, phenylalanine is converted to tyrosine. Tyrosine is then converted to l-dopa, which is then converted to dopamine which is then converted to norepinephrine. The rate-limiting step here is the conversion of tyrosine to l-dopa by tyrosine hydroxylase. Adding large amounts of either tyrosine or phenylalanine won't have much effect on levels of catecholamine neurotransmitters if this enzyme is already saturated. L-dopa has been tried for treating depression in much the same way as has 5-hydroxytryptamine, its analogue along the metabolic route towards the synthesis of serotonin. Perhaps a therapeutic effect is exerted by tyrosine via action as a false transmitter. I don't know.
> > 4) Is it possible for exercise to deplete dopamine and NE stores.
I once had a doctor advise me to not perform any high-intensity exercise (resistance training) while trying to get well as it tended to deplete catecholamines. He said that such exertion was counterproductive towards achieving a remission of depression. Traditional cardiovascular exercise, he said, was O.K.
- Scott
poster:Scott L. Schofield
thread:30864
URL: http://www.dr-bob.org/babble/20000420/msgs/31446.html