Phosphoenolpyruvate Carboxykinase in Cultured Foetal Hepatocytes from the Rat

The involvement of glucocorticoids and insulin in the induction of cytosolic Ppyruvate carboxykinase was studied in cultured hepatocytes derived from 19-day foetal rat liver. Dexamethasone did not increase Ppyruvate carboxykinase activity, but had a synergistic effect on the induction of the enzyme by N6,O2′-dibutyryladenosine 3′,5′-monophosphate (Bt2cAMP). Insulin partially inhibited the induction of Ppyruvate carboxykinase by glucagon, epinephrine or Bt2cAMP. The inhibitory effect of insulin was dose-dependent: significant inhibition was obtained with 0.1 nM insulin. However, the effect of insulin was independent of the dose of glucagon or epinephrine added to the culture medium. The ontogeny of inducibility of Ppyruvate carboxykinase by Bt2cAMP or hormones was tested in foetal hepatocytes after one day of culture. Ppyruvate carboxykinase activity could be induced by epinephrine, glucagon or Bt2cAMP in hepatocytes isolated from day-19, day-16 or day-14 foetuses. Similarly, hepatocytes isolated from day-12 foetal liver were competent to respond to the hormones and Bt2AMP by the accumulation of Ppyruvate carboxykinase. Binding proteins for adenosine 3′,5′-monophosphate (cyclic AMP) were demonstrated in the cytosol from hepatocytes isolated from day-14 and day-19 foetal liver. The results are discussed in terms of the acquisition during hepatocyte differentiation of the competence to respond to hormonal signals, and the role of hormones in the induction of hepatic Ppyruvate carboxykinase at birth.