Activity of alcohol dehydrogenase and aldehyde dehydrogenase in maternal liver, fetal liver and placenta of the near-term pregnant ewe.

The activity of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) was determined in the near-term pregnant ewe. There was little ADH activity in fetal liver (4.4%) and placenta (0.2%) compared with maternal liver. Low KM (microM acetaldehyde) ALDH activity was similar in the three tissues. High KM (mM acetaldehyde) ALDH activity was less in fetal liver (57%) and placenta (16%) compared with maternal liver. These data and the pharmacokinetics of ethanol and its proximate metabolite, acetaldehyde, in the near-term pregnant ewe indicate that ethanol elimination from the maternal-fetal unit is regulated primarily by maternal hepatic ADH-catalyzed biotransformation of ethanol, and low KM ALDH activity in the fetal liver and placenta protects the fetus from exposure to ethanol-derived acetaldehyde, which is produced primarily in the maternal compartment.