Induction of cytosolic aspartate aminotransferase by glucagon in primary cultured rat hepatocytes.

The activity and the mRNA content of cytosolic aspartate aminotransferase (EC 2.6.1.1) were examined in cultured rat hepatocytes. Addition of glucagon (1 × 10 −7 M) in the presence of dexamethasone (1 × 10 −7 M) caused about 2-fold increase in the activity and mRNA content. Dibutyryl cAMP (1 × 10 −4 M) could replace glucagon for this effect. Maximal induction of cytosolic aspartate aminotransferase mRNA was observed 8 h after their additions. Insulin (1 × 10 −7 M) did not inhibit the enzyme induction by glucagon or dibutyryl cAMP. These results suggest that the cytosolic aspartate aminotransferase gene is regulated by cAMP, and not by insulin.