Fatty Acid Synthesis from Glucose and Acetate and the Control of Lipogenesis in Adipose Tissue

Epididymal fat pads of fed and 48 h fasted rats were incubated in vitro with 10 mM glucose and 0, 60, 120, or 10 4 μunits of insulin/ml. A comparison was made of the metabolism of glucose in the absence or presence of 15 mM acetate in the incubation medium. At physiological concentrations of insulin, the addition of acetate increases glucose uptake, glucose oxidation to CO 2 , and incorporation of glucose‐C into fatty acids; concomitantly the rates of glycerol release and lactate production are decreased, and the lactate/pyruvate ratios are lowered. Fatty acid synthesis in the presence of glucose plus acetate was in all cases significantly higher than with glucose alone. It is concluded that, at a given insulin concentration, the conversion of carbohydrate to fat in intact adipose tissue is limited by the tissue's ability to supply acetyl‐CoA for fatty acid synthesis, and not by the enzymes directly engaged in the synthesis of fatty acid from acetyl‐CoA. The effects of acetate were of greater importance in adipose tissue from rats fasted for 48 h than from fed rats. The impairment in lipogenesis caused by fasting appears to be due primarily to a decrease in the tissue's ability to produce acetyl‐CoA from glucose.