This study was performed to investigate the interrelationship between gluconeogenesis and ureagenesis during sepsis. In isolated perfused livers, gluconeogenesis was assessed using either lactate or a combination of lactate, glutamine, and alanine as substrate. Ureagenesis was assessed using either NH4Cl or glutamine plus alanine as substrate. NH4Cl stimulated urea production in livers from both septic and sham-operated control rats. Urea release was approximately 1.2 and 2.0 mg urea nitrogen.g-1.h-1 for 1 and 5 mM NH4Cl, respectively, and was equal for both groups. With amino acids as substrate, urea production was significantly greater in livers from septic animals compared with controls. Phenylephrine stimulated urea production in the sham-operated group by about twofold, whereas in the septic group urea release was slightly inhibited. Gluconeogenesis from lactate was inhibited by NH4Cl (1 and 5 mM) in both groups, with no difference between groups. In contrast to enhanced ureagenesis from amino acids in septic rats, gluconeogenesis was decreased by approximately 24% (P less than 0.5). Similarly, phenylephrine (1 microM) stimulated gluconeogenesis by 13 +/- 1 mumol.g-1.h-1 in sham-operated rats but only by 9 +/- 1 mumol.g-1.h-1 in septic rats (P less than 0.02). These results suggest that hepatic gluconeogenic and ureagenic pathways are intact in sepsis but that altered substrate preference and hormone sensitivity may result in decreased gluconeogenesis in the presence of elevated amino acid levels.