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Brian Collins wrote: > Hello Stefan, your explanation of the effect of Carbidopa is ingenious, > and may well be a part of the story. However I think there is another > more straight-forward explanation: > The level of levodopa in the bloodstream is very low, and is > virtually unaffected by the amount of Sinemet taken by the PWP. The data do not show this. The concentration of levodopa rises quite rapidly to a peak following taking a tablet. The regular tablet is in the blood plasma in it's entirety (99%) at the peak. The decay in concentration is due to metabolic effects including the usage of some of the levodopa by the brain. The CR (controlled release) Sinemet tablets have retarded dissollution and reduce in size slowly at first; then, more rapidly (dependent upon acidity, et cetera of the digestive mixture); then, the diminishing size of the remainder and it's locus in the intestine causes what is left to not be absorbed at all. This is > because a) The Carbidopa does a good job of protecting the levodopa from > attack on its way from the lower intestine to the brain, and b) As > soon as any unprotected levodopa does get into the bloodstream, it is > attacked and broken down. I believe this is mis-information. There is of course a lot of Dopamine in the > bloodstream, but it exists in the body (made by the adrenal gland) for > a totally different reason than the neuro-transmitter role in the brain. Conversion of levodopa to dopamine IS the chemical signal that is the proximate cause of nausea. Carbidopa retards the conversion of levodopa to dopamine. This keeps the amount of levodopa from being reduced to zero much more rapidly than if there is no retardation. (tolcapone and entacapone retard another metabolic enzyme - that being the one that is labeled COMT - to make the levodopa concentration remain high longer in the bloodstream.) This information is basic and needs to be clearly understood. We need to have an accurate, valid, description of the processes and mass transport as well as the chemistry. -- Ron Vetter 1936, '84 PD dz paradise is feeling good, not a place to go [log in to unmask] http://www.ridgecrest.ca.us/~rfvetter