Elevation of Hepatic Phenylalanine Pyruvate Aminotransferase in Rats by Tetraiodoglucagon Is Blocked by Actinomycin D and Cycloheximide

Tetraiodoglucagon caused a severalfold increase in hepatic phenylalanine pyruvate aminotransferase in rats. Cycloheximide, given simultaneously with the tetraiodoglucagon or 4 hr later, nearly completely blocked the elevation of the enzyme. Actinomycin D completely blocked the increase in enzyme activity when it was injected along with tetraiodoglucagon, but had no effect when given four hours after the tetraiodoglucagon. These results indicate that the increased enzyme activity is due to an increased synthesis of enzyme. The formation of new enzyme can be blocked by inhibiting protein synthesis or by inhibiting transcription of genetic information, the latter process apparently being complete within 4 hr after tetraiodoglucagon administration. (Endocrinology 93: 740, 1973)