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Influence of Fasting and Refeeding on Lipogenesis and Enzymatic Activity of Pig Adipose Tissue¹

Division of Nutritional Biochemistry, Department of Animal Science, University of Illinois at Urbana-Champaign, Urbana, Illinois

Fatty acid synthesis and ¹⁴CO₂ production from glucose-U-¹⁴C were virtually abolished in biopsy adipose tissue samples obtained from pigs subjected to a 4-day fast. Refeeding for 2 days fully restored lipogenesis to the prefasting level, and refeeding for 4 days was associated with a twofold overshoot in the capacity for glyceride-glycerol synthesis. No overshoot in fatty acid synthesis could be detected after 4, 6, or 12 days of refeeding. When pigs were refed diets high in protein or fat after a 4-day fast, the restoration of the lipogenic capacity of the adipose tissue was limited to about 50% of that observed in animals refed a high carbohydrate diet. The nonparallel behavior of citrate cleavage enzyme activity and lipogenesis discounts any regulatory role for this enzyme in fatty acid synthesis. Among the NADPH-generating dehydrogenase enzymes studied, malic enzyme appeared more adaptive than the pentose pathway enzymes. The rate of lipogenesis was more closely correlated with the activity of acetyl CoA carboxylase than with any other enzyme assayed. The regulatory implications of these findings in relation to lipogenic control in pig adipose tissue are discussed.

Manuscript received 6 June 1969.