Glucose Metabolism in Isolated Adipocytes from ad Libitum- and Restricted-Fed Lean and Obese Zucker Rats at Two Different Ages

Chronic food restriction in Sprague-Dawley rats has been shown to alter adipose glucose metabolism. In the present study, lean and obese male Zucker rats were food restricted from 5 weeks until either 10 or 26 weeks of age and adipocyte glucose metabolism was measured. Adipocytes from restricted-fed lean and obese Zucker rats converted more glucose to CO₂ and fatty acids than those from their ad libitum-fed counterparts in both the absence and the presence of increasing doses of insulin at 10 weeks of age. At the highest insulin dose, adipocytes from restricted-fed obese rats converted significantly more glucose to CO₂ and fatty acids than did those from restricted-fed lean rats. Basal glyceride-glycerol values were similar in all groups at this age. At the 0.4 and 2.0 ng/ml insulin levels, glyceride-glycerol production was highest in restricted-fed lean rats; restricted-fed obese and ad libitum-fed lean rats had similar values; and ad libitum-fed obese rats had the lowest. At the 20 ng/ml dose, glyceride-glycerol values of restricted-fed rats were higher than those of ad libitum-fed rats. Basal and insulin-stimulated values were compared within each group. Most basal versus insulin-stimulated values were significantly different for the two lean groups. For ad libitum-fed obese rats, only 0 versus 20 ng/ml insulin values were significant. Restricted-fed obese rats had significant increases in 0 versus both 2 and 20 ng/ml insulin values. Restricted-fed obese rats had significantly lower serum insulin levels relative to ad libitum-fed obese rats at 10 weeks of age. Adipocytes from all rats at 26 weeks of age had similar basal rates of conversion of glucose metabolism to all three metabolites. In the presence of insulin, adipocytes from restricted-fed lean rats metabolized significantly more glucose to CO₂ and glyceride-glycerol than adipocytes prepared from the three other groups. Fatty acid production was similar in all groups at each insulin level. Only restricted-fed lean rats showed consistent significant responses to insulin stimulation for the three metabolites. Whether these results are due to age, length of food restriction, or serum insulin levels remains to be determined.