Effect of growth hormone in vitro on phosphofructokinase activity of rat epididymal adipose tissue

The effect of pituitary growth hormone in vitro on phosphofructokinase of epididymal adipose tissue from hypophysectomized rats has been investigated. Of the four key glycolytic enzymes, hexokinase, phosphofructokinase, aldolase, and pyruvate kinase, assayed in the epididymal adipose tissue of hypophysectomized rats, phosphofructokinase was observed to have the least enzyme activity. Phosphofructokinase extracted from epididymal adipose tissue of hypophysectomized rats incubated before homogenization at 37 ° for 10 min with growth hormone (5 μg/ml) had a higher activity (100%) as compared to enzyme preparations from tissues incubated without growth hormone in the medium. The hormone added directly to the homogenates or supernatant extracts did not give any activation. The apparent increase in enzyme activity was not due to de novo synthesis of the enzyme as cycloheximide did not block the effect. Data presented in this communication suggest that as a result of the action of the hormone on intact tissue, there is a stabilization of the enzyme and/or a stable transformation of less active to a more active form of phosphofructokinase. A correlation is observed between the hormonal stimulation of lipogenesis and of phosphofructokinase activity in epididymal adipose tissue.