REGULATION OF HEPATOCYTE GLUTATHIONE BY AMINO-ACID PRECURSORS AND CAMP IN PROTEIN-ENERGY MALNOURISHED RATS

Hepatic glutathione concentration is decreased in protein-energy malnu trition. Malnourished rats are able to replenish hepatic glutathione a fter oral supplementation with L-2-oxothiazolidine-4-carboxylate, a cy steine pro-drug, to levels that are higher than in control rats. These results suggest that, even if a normal amount of amino acids for glut athione synthesis is provided, homeostatic control of glutathione conc entration after protein-energy malnutrition is abnormal. The rate limi ting enzyme for glutathione synthesis, gamma-glutamylcysteine syntheta se, is subject to both short and long term hormonal control. Therefore , we used hepatocytes isolated from weanling rats fed a very low prote in diet (0.5 g protein/100 g diet) or a diet adequate in protein for 2 wk to investigate whether a loss of hormonal control could contribute to abnormal regulation of hepatic glutathione. Glutathione concentrat ion in hepatocytes isolated from protein-energy malnourished rats was 82% lower than in controls. In vitro supplementation of isolated hepat ocytes with oxothiazolidine-4-carboxylate or methionine increased glut athione concentration in hepatocytes from malnourished rats to concent rations equivalent to control cells. However, when hepatocytes were in cubated with cysteine, total glutathione in malnourished rats exceeded that of controls. Treatment of cells from control rats with 50 nmol/L glucagon or 1 mmol/L db-cAMP decreased glutathione concentration by 2 5-43%. In contrast, the glutathione concentration in hepatocytes of ra ts fed the low protein diet did not respond to treatment with glucagon or db-cAMP. These data indicate that glutathione synthesis is insensi tive to regulation by cAMP in rats with protein-energy malnutrition. T his loss of responsiveness to hormonal control may contribute to the a bnormal homeostatic regulation of hepatic glutathione observed in prot ein-energy malnutrition.