Effects of Undernutrition and Refeeding on Enzyme Activities and Rates of Glucose Catabolism in Rat Epididymal Adipose Tissue

The effects of partial caloric restriction and refeeding on aspects of glucose metabolism in rat epididymal adipose tissues were compared to the effects of total fasting and refeeding. Unlike total fasting, semi-starvation (produced by feeding half the amount of diet consumed daily by fed rats) did not result in decreased rates of fatty acid synthesis until 7 days, while the specific activities of malic enzyme (ME), citrate cleavage enzyme (CCE) and glucose-6-phosphate dehydrogenase (G-6-PD) remained at fed levels throughout 7 days of semi-starvation. When 2-day semi-starved rats were refed for 2 days, rates of incorporation of labeled glucose into fatty acids were increased two- to threefold as compared to fed or semi-starved rats before refeeding. However, when 7-day semi-starved rats were refed, rates of incorporation of glucose into carbon dioxide, triglyceride glycerol, as well as fatty acids were increased between twofold and sevenfold as compared to fed rats. Specific activities of ME, CCE, G-6-PD and 6-phosphogluconate dehydrogenase were also increased 2- to 3.5-fold above fed levels in 7-day-semi-starved-refed rats. Thus, partial caloric restriction had smaller or no immediate effects on the capacity of adipose tissue to metabolize glucose, in contrast to the easily-demonstrated depression of in vitro lipogenesis and glycolysis resulting from total starvation. Upon refeeding, however, the rebound effects on rat adipose tissue lipogenesis rates as well as on lipogenic enzyme activities were more pronounced after prolonged partial caloric restriction than after shorter periods of caloric restriction or total fasting.