[QUOTE=zanpar321;1127355]
Quote:
Originally Posted by lurkingforacure
My understanding is that the BBB isn't really quite 100% impermeable. For example, those that take L-Dopa via the Hinz protocol take large quantities of L-Dopa and thus some crosses the BBB to be made into dopamine in the brain, but most gets peed out. Sinemet allows much more to cross the BBB by adding Carbidopa so much less L-Dopa is required to have an effect.
Regarding Thiamine, rather than saturating our body with Thiamine, it makes more sense to get IM thiamine injections or even take liposomol thiamine which allows more to get absorbed. Liposomol allows it to be protected in lecithin spheres until it gets further down the gut and thus more gets absorbed. What seems important is to get it into the brain before the body breaks it down and it gets removed.
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l-dopa passes the BBB via active transport, the more L-DOPA in the blood, the more will cross the BBB. but even with carbidopa which inactivates an enzyme which breaks down l-dopa in the blood, less than 5% gets into the brain and then enzymes there break it down into something other than dopamine so very little becomes dopamine.
Carrier-mediated transport enables molecules with low lipid solubility to traverse the blood-brain barrier. Glucose from blood enters the brain by a transport protein. Glucose is the primary energy substrate of the brain. Glucose transport protein (GLUT-1) is highly enriched in brain capillary endothelial cells. These transporters carry glucose molecules through the blood brain barrier. Although rare, patients with Glut-1 deficiency (caused by genetic mutations) can have severe learning difficulties. Low glucose sugar levels in the cerebrospinal, but not in the blood, will identify the condition.
The essential amino acids cannot be synthesized by the brain and, therefore, must be supplied from protein breakdown and diet. Phenylalanine, leucine, tyrosine, isoleucine, valine, tryptophan, methionine and histidine, which are essential amino acids, and also the precursor of dopamine, L-DOPA, enter the brain as rapidly as glucose. These amino acids are transported into the brain by the leucine-preferring or the L-type transport proteins. These compounds compete with each other for entry into the brain. Therefore, an elevation of plasma level of one will inhibit uptake of the others. This competition may be important for certain metabolic diseases such as phenylketonuria (PKU), where high levels of phenylalanine in plasma reduce brain uptake of other essential amino acids.
Small neutral amino acids, such as alanine, glycine, proline and GABA (gamma-aminobutyric acid), are markedly restricted in their entry into the brain. These amino acids are non-essential amino acids and are transported by alanine-preferring or A-type transport protein. The A-type transport protein is not present on the luminal surface of the blood brain barrier. In contrast, these small neutral amino acids appear to be transported out of the brain across the blood-brain-barrier.
http://neuroscience.uth.tmc.edu/s4/chapter11.html