L-DOPA is used to replace dopamine lost in Parkinson's disease because dopamine itself cannot cross the blood-brain barrier where its precursor can. However, L-DOPA is converted to dopamine in the periphery as well as in the CNS, so it is administered with a peripheral DDC (dopamine decarboxylase) inhibitor such as carbidopa, without which 90% is metabolised in the gut wall, and with a COMT inhibitor if possible; this prevents about a 5% loss. The form given therapeutically is therefore a prodrug which avoids decarboxylation in the stomach and periphery, can cross the blood-brain barrier, and once in the brain is converted to the neurotransmitter dopamine by the enzyme aromatic-L-amino-acid decarboxylase.

Side Effects

Possible side effects include:

Hypotension, especially if the dosage is too high.
Arrhythmias, although these are uncommon.
Nausea, which is often helped by taking the drug with food, although protein interferes with drug absorption.
Gastrointestinal bleeding.
Disturbed respiration. This is not always harmful, and can actually benefit patients with upper airway obstruction.
Hair loss.
Confusion.
Extreme emotional states, particularly anxiety, but also excessive libido.
Vivid dreams and/or fragmented sleep.
Visual and possibly auditory hallucinations. It can reveal dementia that was previously subclinical.
Effects on learning. There is some evidence that it improves working memory, while impairing other complex functions.
Sleepiness and sleep attacks.
a condition similar to amphetamine psychosis.

Although there are a number of side-effects associated with L-DOPA, particularly psychiatric ones, it has fewer than other Parkinson's drugs, including anticholinergics, selegiline, amantadine, and dopamine agonists.

More serious are the effects of chronic L-DOPA administration, which include:

End-of-dose deterioration of function.
On/off oscillations.
Freezing during movement.
Dose failure (drug resistance).
Dyskinesia at peak dose.

Clinicians will try to avoid these by limiting L-DOPA dosages as far as possible until absolutely necessary.

Synthesis

L-Dopa is produced from the amino acid tyrosine by the enzyme tyrosine hydroxylase. It is also the precursor molecule for the catecholamine neurotransmitters dopamine and norepinephrine (noradrenaline), and the hormone epinephrine (adrenaline). The prefix L- references its property of levorotation (compared with dextrorotation or D-DOPA).

Read more at Wikipedia.org

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Quantum sufficit: just enough
From American Family Physician, 10/1/05 by Lisa Graham

* New memories may erase old cravings, according to a study published in the Proceedings of the National Academy of Sciences. Researchers found they could influence people to crave strawberry ice cream less after implanting false suggestions about bad childhood experiences with it. The scientists gathered data from more than 200 volunteers and then persuaded them to believe they got sick from strawberry ice cream as children. As a result, about 40 percent of the participants believed the false memory, and most of those persons lowered their preference for the ice cream on a later survey. The same study was performed with chocolate chip cookies; however, it did not yield the same outcome. (PNAS, August 3, 2005)

* Can a popular "club drug" help relieve the symptoms of Parkinson's disease? A group of researchers found that the drug methylenedioxymethamphetamine, also known as Ecstasy, eased Parkinson's-like symptoms in mice. Although the team has not researched the drug's effect on humans, they are hopeful that this will lead to new treatment opportunities for people with tremors and stiffness caused by Parkinson's disease. Researchers found even greater results when this drug was combined with the current Parkinson's disease drug, levodopa. (Nature, August 2, 2005)

* "Like mother, like daughter" is true when it comes to cohabitation of unmarried couples. A study by Ohio State University found that girls whose mothers reported cohabitation were more likely to cohabit themselves. Data for the study came from the National Longitudinal Survey of Youth, which surveyed men and women who were 14 to 22 years of age in 1979. Researchers talked with the participants annually until 1994 and every two years from 1996 forward. They also surveyed the participants' children. Girls with cohabiting mothers were 57 percent more likely to live with a partner and did so at a younger age. Authors believe that the girls modeled their behavior after their mothers. (Ohio State University Research News, August 15, 2005).

* Work it out! According to researchers at the University of Bristol in England, on the days workers exercised for at least 31 to 60 minutes during their shift, they returned to their desks more productive and easier to get along with than on days they didn't exercise. The six-week study followed 210 men and women 23 to 57 years of age who worked out at an on-site gym at least one day each week. Two in three participants reported improvements in at least one area of mood, energy, productivity, or efficiency while on the job. (The Washington Post, July 5, 2005).

* Is smoking more expensive than originally thought? The Centers for Disease Control and Prevention reports that premature death by way of lung cancer, heart disease, and other smoking-related illnesses cost the United States about $92 billion in lost wages between 1997 and 2001. On average, men lose 3.3 million years of life and women lose 2.2 million years because of smoking. The lost productivity and smoking-related health care expenses cost the nation more than $167 billion annually. (Morbidity and Mortality Weekly Report, June 30, 2005).

* Consumers can now add one more thing to their shopping lists: medical advice. ABC News reports that some supermarkets, retail chains, and pharmacies now house MinuteClinics. In these small kiosks, shoppers can get advice and remedies for minor ailments from a nurse practitioner without having to make appointments or spend time in waiting rooms. With the help of specially designed software, nurse practitioners are able to identify and treat 24 common illnesses and infections, including pink eye and bronchitis. However, clinic operators say that these MinuteClinics are no substitute for family physicians. (ABC News, June 21, 2005)

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