We examined the effect of a 240 min intraportal infusion of a nonlethal dose of Escherichia coli endotoxin (.21 g x kg(-1) x min[-1]) on hepatic amino acid and glucose metabolism in chronically catheterized 42 h fasted conscious dogs (n = 8). Hepatic metabolism was assessed using tracer (3-[3H]glucose [U-14C]alanine) and arteriovenous difference techniques. After endotoxin administration net hepatic glucose output increased twofold. Arterial plasma insulin levels decreased by 25%, whereas arterial plasma glucagon and cortisol levels increased 10- and 6-fold, respectively. Arterial lactate levels increased 6.4-fold, whereas net hepatic lactate uptake was not increased. Arterial alanine levels (1.6-fold) and net hepatic alanine uptake (1.3-fold) increased, whereas net hepatic alanine fractional extraction was unaltered. In contrast, the arterial levels of the other gluconeogenic amino acids (glutamine, glycine, serine, and threonine) decreased. Despite this decrease, net uptake of these amino acids by the liver did not decrease, because net hepatic amino acid fractional extraction increased. Total net hepatic gluconeogenic precursor uptake was unaltered (1.1 +/- .1 to 1.3 +/- .3 mg x kg(-1) x min(-1) expressed in glucose equivalents). In summary, gluconeogenesis does not increase after endotoxin administration. Thus, an increase in net hepatic glycogenolysis accounts for the majority of the increase in hepatic glucose production. The lack of an increase in alanine fractional extraction, despite hyperglucagonemia and a rise in the fractional extraction of other gluconeogenic amino acids, suggests that endotoxin specifically impairs hepatic alanine entry in vivo.