Re: How is alcohol metabolished in the fetus?

Dear Cathy,

Thanks for the question. The short answer is that fetal alcohol metabolism is essentially similar to that found in adult tissues, because the same enzymes are present. Ethanol is first oxidised to acetaldehyde by an enzyme called alcohol dehydrogenase. Acetaldehyde is a very toxic compound-it is teratogenic, meaning it can cause developmental defects, and is also largely responsible for the headache experienced after drinking to excess. Acetaldehyde is further oxidised to acetate by the enzyme acetaldehyde dehydrogenase. The acetate can then be used for energy metabolism.

However, fetal alcohol metabolism is a complicated process. The placenta contains high levels of alcohol and acetaldehyde dehydrogenases, but they are not high enough to remove all of these compounds if intake is high, so in fact a lot of the alcohol is metabolised to acetaldehyde in the placenta, but this is then passed to the fetus. Alcohol dehydrogenase is also found in 2 forms in 2 different locations in the cell, only one of which increases substantially in response to alcohol. And of course because the fetus is so small and the tissues are still developing, the activity of these enzymes may not be sufficient to cope with an excess of alcohol. In addition the oxidation of ethanol produces high levels of reduced molecules in the cell (such as NADH). This has to become reoxidised for metabolism to continue and so there can be negative effects on energy metabolism in the fetal cells. This explains the small size of children born with fetal alcohol syndrome. The high concentrations of reducing molecules can also lead to the production of toxic oxygen species, which damage cell membranes, proteins and DNA.

If you want to know more about fetal alcohol syndrome and metabolism, I recommend these 3 sites:

http://www.nau.edu/fronske/fas.h tml

http://w eb.mit.edu/newsoffice/tt/1997/oct29/alcohol101.html

http:/ /www.babyonline.com/library/prenatal/foresight/alc.html

And if you want to read scientific papers on the subject, go to:

http://www.biomednet.com/db/medl ine

and enter a search such as "fetal AND alcohol AND metabolism".

(free registration is needed for this last site).

Neil Saunders