Studies in humans have indicated that the folate deficiency of chronic alcoholism is due to a toxic effect of ethanol to deplete folate as well as to an inadequate dietary intake of folate. The mechanism of this toxic effect is not completely understood and studies using an animal model need to be conducted. The suitability of the rat as a possible animal model for the induction of folate deficiency by chronic ethanol use will be tested. Rats will be used because preliminary studies have shown that acute ethanol treatment induces a decrease in plasma folate levels similar to that observed in humans. Feeding experiments using ethanol with a nutritionally-sufficient liquid diet or a folate-deficient liquid diet will be employed in a pairfed manner to assess the effects of ethanol. Blood ethanol levels and hematologic and folate status will be determined periodically. Folate status will be measured directly by microbiological analysis of blood, liver, kidney, and urine samples or indirectly by the urinary excretion of formate. An assay utilizing high pressure liquid chromatography for the determination of individual folate compounds will be used to measure the ethanol-induced changes in tissue folates. Preliminary studies have shown that the decreased plasma folate levels after acute ethanol treatment result from increased urinary folate excretion. Hence, this study will evaluate the role of increased urinary folate excretion as a mechanism for the chronic ethanol-induced folate deficiency. In the rat feeding experiment, urinary folate levels will be closely monitored. Furthermore, studies in ethanol-consuming human subjects will be conducted to test whether increased urinary folate excretion is a means by which plasma folate levels are decreased. Ethanol in an acute oral dose will be administered to human volunteers and the folate levels in plasma and urine determined for a 24 hour period. Finally, the mechanism for the increased urinary excretion in rats will be studied by testing the effect of ethanol on plasma folate binding in vivo using a radiobinding assay, on folate reabsorption by the kidney using clearance studies, and on folate binding in vitro by renal tubular membranes using a radiobinding assay. Determination of the mechanism of the increased urinary folate excretion will help to further understanding of the production of the folate deficiency that is very common in chronic alcoholics.
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