Posted by SLS on August 18, 2006, at 20:41:14
In reply to Re: Sibutramine (Meridia) - Day 12 » SLS, posted by mayzee on August 18, 2006, at 19:59:56
> Scott, thanks for the explanation; I didn't know that all those neurotransmitters were monoamines! If you don't mind continuing... so what is the "monoamine oxidase" that's in MAOI (vs. the monoamine you just described to me)?
At some point, the neuron must control the amount of the monoamine neurotransmitter it stores and prevent too much from collecting. It therefore uses an enzyme to metabolize and break-down the excess. This enzyme is known as monoamine oxidase. If this enzyme is inhibited by the MAOI drug and prevented from performing its task, the levels of the neurotransmitter are permitted to rise. It is thought that this increase in the availability of monoamine neurotransmitters is important in the mechanism of action of MAOI antidepressants.
There are two forms of the MAO enzyme. There is MAO-A and MAO-B. MAO-A is responsible for metabolizing norepinephrine and serotonin while MAO-B is responsible for metabolizing dopamine. Some MAOI drugs are selective for one type over the other. Emsam (selegiline) is selective for MAO-B at lower dosages, but becomes non-selective at higher dosages. Moclobemide is selective for MAO-A. Some researchers believe that MAO-A is more important for treating depression. A MAOI can be either reversible or irreversible. Most of the MAOIs in current use are irreversible. Once they attach themselves to the MAO enzyme, the enzyme is permanently destroyed. The body must synthesize a new enzyme to replace it. This is why one must wait 2 weeks after discontinuing an irreversible MAOI before beginning another antidepressant. Moclobemide is different. It is reversible. It does not damage the enzyme while it is attached. When the drug concentration decreases, the drug detaches from the enzyme and allows it to function again. Also, other molecules competing for the MAO enzyme can bump into the drug and knock it off. This allows users of moclobemide to eat modest amounts of tyramine without provoking a hypertensive reaction.
- Scott
poster:SLS
thread:673646
URL: http://www.dr-bob.org/babble/20060818/msgs/677935.html