Abstract. Replacement of dietary triglycerides containing long-chain fatty acids (LCFA) by triglycerides containing medium-chain fatty acids (MCFA) markedly reduced the capacity of alcohol to produce fatty liver in rats. After 24 days of ethanol and MCFA, the increase in hepatic triglycerides was only 3 times that of controls, whereas an 8-fold rise was observed after ethanol and LCFA. The triglyceride fatty acids that accumulated in the liver after feeding of ethanol with MCFA contained only a small percentage of the MCFA; their composition also differed strikingly from that of adipose lipids.To study the mechanism of the reduction in steatosis, we compared oxidation to CO2 and incorporation into esterified lipids of 14C-labeled chylomicrons or palmitate-14C (representing LCFA), and of octanoate-14C (as MCFA) in liver slices and isolated perfused livers, in the presence or absence of ethanol. Ethanol depressed the oxidation of all substrates to CO2; MCFA, however, was much more oxidized and reciprocally much less esterified than LCFA, with a 100-fold difference in the ratio of esterified lipid-14C to 14CO2. Furthermore, in hepatic microsomal fractions incubated with a-glycerophosphate, octanoate was much less esterified than palmitate. This propensity of MCFA to oxidation rather than esterification represents a likely explanation for the reduction in alcoholic steatosis upon replacement of dietary LCFA by MCFA.

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A B S T R A C T Ketonuria has been observed in alcoholics. To study the mechanism of this effect, healthy, volunteers were given adequate diets (36% of calories as lipid and 15% as protein) for 18 days, with isocaloric replacement of carbohydrate (46% of calories) by either ethanol or additional fat. The latter resulted in a high fat diet, with 82% of calories as lipid. After about 1 wk of alcohol, massive and persistent ketonuria developed. Compared with the control period, there was a 30-fold increase in fasting blood acetoacetate and P-hydroxybutyrate (P < 0.001). With the high fat diet, acetoacetate and P-hydroxybutyrate increased 8-to 10-fold (P < 0.001). In the postprandial state, ethanol also induced hyperketonemia, but less markedly than when ethanol followed an overnight fast. With low fat diets (5% of calories), alcohol (46% of total calories) did not induce ketonuria or hyperketonemia, suggesting that a combination of alcohol and dietary fat is necessary. The addition of alcohol to rat liver slices did not affect ketogenesis. In rats pretreated with alcohol for 3 days, however, ketonemia developed, hepatic glycogen was decreased, and liver slices (incubated with palmitate-'4C and glucose) had a significant increase in acetoacetate production, when compared to carbohydrate pretreated controls. Alcohol pretreatment or addition of alcohol in vitro had no effect on acetoacetate utilization by rat diaphragms, and decreased only slightly the conversion of P-hydroxybutyrate--4C to "CO2. Thus, the hyperketonemia and ketonuria observed after alcohol consumption cannot be attributed to an immediate effect of alcohol, but is the consequence of a delayed change in intermediary metabolism characterized by increased hepatic ketone production from fatty acids, possibly linked to ethanol-induced glycogen depletion and depression of citric acid cycle activity.

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