The effect of insulin and glucocorticoids on the synthesis and degradation of phosphoenolpyruvate carboxykinase (GTP) in rat adipose tissue cultured in vitro

Epididymal adipose tissue from the rat was maintained in culture for periods of up to 96 h. After an initial decrease in protein synthesis during the first 24 h of culture, the adipose tissue recovered its capacity to synthesize and accumulate proteins of a relatively large size. The activity of phosphoenolpyruvate carboxykinase decreased in a parallel manner, but increased again after 24 h of incubation of the tissue in culture, to a value twice that noted in the tissue in vivo. This increase in enzyme activity was due to an increase in its rate of synthesis. Both insulin and dexamethasone (9α fluoro 16α methyl 11β,17,21 trihydroxypregna 1,4 diene 3,20 dione) inhibited phosphoenolpyruvate carboxykinase synthesis, but dexamethasone also decreased total protein synthesis. The half life of phosphoenolpyruvate carboxykinase in adipose tissue cultured in vitro was 5-7 h and was not altered by insulin or dexamethasone. It is concluded that both insulin and glucocorticoids lower the activity of phosphoenolpyruvate carboxykinase in rat adipose tissue by decreasing its rate of synthesis.