1. The influence of a deficiency or surplus of thiamin in the diet on voluntary ethanol consumption, ethanol elimination rate and blood acetaldehyde concentration was studied in rats.
2. Both the high-thiamin diet containing 20 mg thiamin hydrochloride/kg and the thiamin deficient diet containing no measurable thiamin produced obvious functional effects on thiamin metabolism in rat tissues after 4 weeks as demonstrated by measurements of the blood transketolase (sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate glycolaldehyde-transferase; EC 18.104.22.168) activity and the extent of thiamin pyrophosphate-stimulation of the enzyme.
3. During the first week on the test diets the prospective ethanol free-choice groups had 1.72 M-ethanol as their only drinking-fluid. Subsequently they had a choice between ethanol and tap water for three weeks. During the free-choice period the rats on the high-thiamin diet drank only one-fifth as much ethanol as the rats given the optimum diet with 4 mg thiamin hydrochloride/kg.
4. The thiamin-deficient rats showed a significant tendency to increase ethanol drinking, when intake was expressed relative to total energy intake, but their intake of ethanol on a g/kg body-weight basis was approximately the same as that of the group given the optimum-diet.
5. The observed differences in voluntary ethanol drinking associated with different levels of dietary thiamin cannot be explained by changes in the ethanol elimination rate or the acetaldehyde accumulation in blood during the oxidation of ethanol.