Further Studies on the Time Course of Rerepression 1 of Two Rat Liver Enzymes

Summary

Rerepression of G6PD, 6PGD, and ME can be accomplished by feeding a high-fat diet to starving rats. When such regimen is followed, a second episode of starvation-refeeding will no longer cause “increased inducibility” of these enzymes. Treatment of the rats with 8-azaguanine during the feeding of the high-fat diet prevented the effect of the high-fat diet on G6PD inducibility, decreased the effect on ME inducibility, but had very little effect on 6PGD inducibility. The results indicate that transcriptional rerepression requires exogenous fat and de novo RNA synthesis, but that 6PGD can be rerepressed without de novo RNA synthesis. The results further indicate that the de novo RNA synthesis necessary for the rerepression of G6PD and ME occurs during the second day of refeeding and coincides with the time course of de novo RNA synthesis requirement for the enzyme overshoot.