The proposed research will evaluate several mechanisms for folate deficiency in chronic alcoholism. Folate deficiency is the most common laboratory sign of malnutrition in chronic alcoholic patients, affecting nucleoprotein synthesis and cellular turnover in all tissues, especially the bone marrow and small intestine. Although dietary lack is a major cause of folate deficiency in the binge-drinking alcoholic, considerable evidence indicates that other factors contribute to this condition. These factors include decreased intestinal folate absorption and alterations in the hepatobiliary circulation of folates. We will use the miniature pig as an experimental model for our studies since this species is known to ingest alcohol ad libitum to intoxicating blood levels, and since we have found that the regulation of folate absorption in the pig is similar to that described in humans. In pigs fed ethanol for 3 months and in a paired-fed control group, folate absorption will be measured by the triple lumen perfusion technique with permanent jejunal stomas for tube access. This approach will permit assessment of hydrolysis of labeled polyglutamyl folates and uptake of the labeled monoglutamyl folates. In vitro, mucosal tissue will be used to measure the activities of intestinal folate conjugases and the binding and transport of labeled folate by brush border vesicles. The kinetics of the enterohepatic folate cycle will be measured in pigs with jejunal and ileal stomas and cannulated bile ducts. This will permit measurement of intestinal absorption while an electronic stream splitter will sample continuously precise fractions of the bile following introduction of labeled folates into the intestine. This model will permit measurements in each group of daily biliary folate secretion and the bile folate pool size, and, with the introduction of labeled folic acid, the fractional biliary appearance of absorbed folate and the t 1/2 of the biliary folate pool. Hepatic folate binding and metabolism will be measured in liver removed after completion of the biliary studies. In vitro studies will include measurement of uptake of labeled folate by isolated liver plasma membranes from chronic ethanol fed and control fed animals. These studies will permit conclusions on the effect of chronic and acute ethanol exposure on a variety of steps required in the intestinal absorption and hepatobiliary metabolism of folates. Overall, the studies will permit further knowledge of the mechanisms of deficiency of this vitamin in alcoholic patients.
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