Since administration of ATP-MgCl2 following trauma and hemorrhagic shock improves tissue perfusion as well as cell and organ function, the aim of this study was to determine whether this agent has any salutary effects on the hepatic rate-controlling enzymes specific for gluconeogenesis, such as phosphoenolpyruvate carboxykinase (PEPCK), and for glycolysis, such as pyruvate kinase (PK), under such conditions. To study this, rats underwent a 5-cm midline laparotomy (i.e., trauma-induced) and were bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% of maximum bleed out volume was returned in the form of Ringer's lactate (RL). The animals were then resuscitated with 3 times the volume of shed blood with RL over 45 min, followed by 2 times RL with ATP-MgCl2 (50 micromol/kg body wt.) or an equivalent volume of normal saline over 95 min. Hepatic PEPCK, PK and glucokinase activities were determined 4 h after the completion of resuscitation. The mRNA levels of PEPCK and PK in the isolated hepatocytes were determined by Northern blot analysis. The results indicate that glucokinase activity was not significantly altered after hemorrhage, irrespective of ATP-MgCl2 treatment. Although the mRNA levels of PEPCK were similar in all groups, PEPCK activity decreased significantly after hemorrhage. ATP-MgCl2 treatment, however, restored PEPCK activity. Hemorrhage resulted in an increase in PK activity and its mRNA. ATP-MgCl2 treatment significantly decreased PK activity and the mRNA. Thus, up-regulation of the gluconeogenic enzyme, PEPCK, and down-regulation of the glycolytic enzyme, PK, by ATP-MgCl2 may be responsible, in part, for the beneficial effects of this agent following trauma-hemorrhage and resuscitation.