Role of fatty acid synthesis in the control of insulin-stimulated glucose utilization by rat adipocytes.

A decreased capacity for fatty acid synthesis is associated with a decreased insulin effect on glucose metabolism in large fat cells and fat cells from rats fed a high-fat diet. We have investigated the relationship between these processes by specifically inhibiting fatty acid synthesis with (-)-hydroxycitrate (2.5 mM), an inhibitor of citrate cleavage enzyme, and cerulenin (0.05 mM), an inhibitor of fatty acid synthetase. (-)-Hydroxycitrate and cerulenin decreased maximally insulin-stimulated fatty acid synthesis from [6-(14)C]glucose to 10% and 25% of controls, respectively, while only (-)-hydroxycitrate decreased basal values. Oxidation of [1-(14)C]glucose in the presence of insulin was markedly depressed by each inhibitor. Thus, the percent increase over basal value was decreased from 540% in controls to 151% and 154% by (-)-hydroxycitrate and cerulenin, respectively. In contrast, oxidation of [6-(14)C]glucose was slightly enhanced by both inhibitors. Thus, oxidation of glucose via the pentose shunt was reduced, while Krebs cycle oxidation was unaffected. Basal and insulin-stimulated incorporation of [1-(14)C]glucose and [6-(14)C]glucose into glyceride-glycerol and basal lactate production was unchanged by the inhibition of fatty acid synthesis. Insulin-stimulated lactate production was halved by the inhibition of fatty acid synthesis. Total glucose utilization, as assessed by measuring the disappearance of glucose from the medium, was not detectably changed by inhibiting fatty acid synthesis under basal conditions, but insulin-stimulated values were decreased to 52% and 64% of control by (-)-hydroxycitrate and cerulenin, respectively. This occurred despite the fact that neither agent affected the initial rate of 2-deoxyglucose uptake, or glucose-6-phosphate dehydrogenase or 6-phosphogluconate dehydrogenase activities. These data therefore provide direct evidence that a limitation of the fatty acid synthetic pathway decreases the ability of insulin to stimulate both pentose shunt glucose oxidation and overall glucose utilization, but not Krebs cycle oxidation or glyceride-glycerol synthesis. The enzymatic capacity of the fat cell for fatty acid synthesis is therefore an important determinant of insulin-stimulated glucose utilization.-Fried, S. K., M. Lavau, and F. X. Pi-Sunyer. Role of fatty acid synthesis in the control of insulin-stimulated glucose utilization by rat adipocytes.