DIFFERENTIAL TIME-COURSE OF LIVER AND KIDNEY GLUCOSE-PHOSPHATASE ACTIVITY DURING LONG-TERM FASTING IN RAT CORRELATES WITH DIFFERENTIAL TIME-COURSE OF MESSENGER-RNA LEVEL

We have studied the role of Glc6Pase mRNA abundance in the time course of Glc6Pase activity in liver and kidney during long-term fasting in rat. Refered to the mRNA level in the fed state, Glc6Pase mRNA abundan ce was increased by 3.5 +/- 0.5 and 3.7 +/- 0.5 times (mean +/- S.E.M. , n = 5) in the 24 h and 48 h-fasted liver, respectively. Then, the li ver Glc6Pase mRNA was decreased to the level of the fed liver after 72 and 96 h of fasting (1.0 +/- 0.3 and 1.4 +/- 0.3). In the kidney, Glc 6Pase mRNA abundance was increased by 2.7 +/- 1.0 and 5 +/- 1.2 times at 24 and 48 h of fasting, respectively. Then, it plateaued at the lev el of the 48 h fasted kidney after 72 h and 96 h of fasting (4.5 +/- 1 .0 and 4.3 +/- 1.0). After 24 and 48 h-refeeding, the abundance of Glc 6Pase mRNA in 48 h-fasted rats was decreased to the level found in the liver and kidney of fed rats. The time course of the activity of Glc6 Pase catalytic subunit during fasting and refeeding was strikingly par allel to the time course of Glc6Pase mRNA level in respective tissues. These data strongly suggest that the differential expression of Glc6P ase activity in liver and kidney in the course of fasting may be accou nted for by the respective time course of mRNA abundance in both organ s.