Ontogeny of the activity of alcohol dehydrogenase and aldehyde dehydrogenases in the liver and placenta of the guinea pig.
The objectives of this study were to elucidate the ontogeny of the activity of alcohol dehydrogenase (ADH), low Km aldehyde dehydrogenase (ALDH) and high Km ALDH in the liver and placenta of the guinea pig, and to determine the relationship between the relative activity of each enzyme in the guinea pig maternal-placental-fetal unit and the disposition of ethanol and its proximate metabolite, acetaldehyde. The enzyme activities were determined in maternal liver, fetal liver, and placenta of the guinea pig at 34, 50, 60 and 65 days of gestation (term, about 66 days), in the liver of the 2-day-old neonate, and in adult liver. There was low ADH activity in fetal liver and placenta throughout gestation and in neonatal liver. The fetal liver low Km ALDH activity increased progressively and, at 60 days of gestation, was similar to adult liver activity, as was also the case for neonatal liver enzyme activity. Placental low Km ALDH activity was less than adult liver activity throughout gestation. Fetal hepatic high Km ALDH activity increased during gestation, but was less than adult liver activity, as was also the case for neonatal liver enzyme activity. Placental high Km ALDH activity was low throughout gestation. For oral administration of 0.5 g ethanol/kg maternal body weight to pregnant guinea pigs at mid-gestation (34 days), the maternal blood and fetal body ethanol concentration-time curves were similar. Acetaldehyde was measurable in maternal blood and fetal body at similar concentrations, which were 100- to 1000-fold less than the respective ethanol concentrations. The major difference in the disposition of ethanol and acetaldehyde at near-term pregnancy, compared with mid-gestation, was the lack of measurable acetaldehyde in fetal blood. These results indicate that the guinea pig fetus throughout gestation has virtually no capacity to oxidize ethanol, and its duration of exposure to ethanol is regulated by maternal hepatic ADH-catalyzed biotransformation of ethanol. The fetus, however, appears to have increasing low Km ALDH-dependent capacity to oxidize ethanol-derived acetaldehyde during development, and would appear to be increasingly protected from exposure to acetaldehyde as gestation progresses.
Department of Pharmacology and Toxicology, Faculty of Medicine, Queen's University, Kingston, Ontario, Canada.
S E
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Card
S F
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Tompkins
J F
JF
Brien
D000079:Acetaldehyde / Q000378:metabolism; D000426:Alcohol Dehydrogenase / Q000378:metabolism*; D000444:Aldehyde Dehydrogenase / Q000378:metabolism*; D000818:Animals; D000431:Ethanol / Q000378:metabolism; D005260:Female; D005865:Gestational Age; D006168:Guinea Pigs; D008099:Liver / Q000196:embryology / Q000201:enzymology*; D008431:Maternal-Fetal Exchange; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy
D000431:Ethanol; D000426:Alcohol Dehydrogenase; D000444:Aldehyde Dehydrogenase; D000079:Acetaldehyde