A possible physiological role for glyceroneogenesis in rat adipose tissue.

Pyruvate decreased the rate of free fatty acid release from rat epididymal adipose tissue incubated in vitro by increasing free fatty acid esterification. The magnitude of the pyruvate effect, tested in tissues from fasted, adrenalectomized, or diabetic rats, closely correlated both with the rate of glyceride-glycerol labeling from radioactive pyruvate and with the activity of P-enolpyruvate carboxykinase. The addition of 25 mu pyruvate to adipose tissue from 24-hour fasted rats produced a X-fold increase in free fatty acid esterification. At a lower concentration (0.25 mu) pyruvate had no effect on free fatty acid esterification but butyrate added in equimolar concentrations caused a 50% increase in ester&ation of free fatty acids in tissue from fasted animals. These findings support the role of P-enolpyruvate carboxykinase as a regulatory enzyme in the glyceroneogenic sequence and suggest that glyceroneogenesis is important in adipose tissue for the maintenance of free fatty acid esterification. The role of the adrenals and of insulin in regulating the activity of rat adipose tissue P-enolpyruvate carboxykinase is also presented. Diabetes increased the activity of this enzyme in adipose tissue and liver but adrenalectomy superimposed upon diabetes caused a further increase in adipose tissue P-enolpyruvate carboxykmase activity and a reduction in the activity of the hepatic enzyme. Both insulin and triamcinolone reduced the activity of adipose tissue P-enolpyruvate carboxykinase in adipose tissue from diabetic-adrenalectomized rats but only when the two hormones were administered simultaneously was the level of the enzyme reduced to normal.