Control of phosphoenolpyruvate carboxykinase in brown adipose tissue of infant rats.

Activity of phosphoenolpyruvate carboxykinase (PEPK) in brown adipose tissue (BAT) of infant rats is high and is depressed by a single injection of corti-costeroid or insulin. Both hormones inhibit synthesis of the enzyme in BAT and increase it in liver. Fatty acid synthetase activity is enhanced by these hormones, but only in BAT. It is suggested that corticosteroids may act via insulin release, since both blood glucose and blood insulin levels rise after steroid injection. The difference in response between BAT and liver is ascribed to the difference in adenyl cyclase response in the two tissues.