Growth hormone (GH), which is well known as an anabolic agent in systemic protein metabolism but has catabolic effects on the carbohydrate metabolism in the liver, was administered to normal rabbit to investigate its effects on the hepatic energy metabolism. The changes in arterial ketone body ratio (AKBR: acetoacetate/3-hydroxybutyrate), which reflects the hepatic mitochondrial redox state ([NAD+]/[NADH]), after GH injection was studied as an indicator of the hepatic energy metabolism. GH was administered to normal rabbit at the doses of 50 micrograms/kg (GH-50 group), 100 micrograms/kg (GH-100 group) and 200 micrograms/kg (GH-200 group) by intravenous bolus injection. In the GH-50, GH-100 and GH-200 groups, AKBR decreased significantly from 1.40 +/- 0.09 to 0.94 +/- 0.05, from 1.19 +/- 0.11 to 0.83 +/- 0.14, and from 1.19 +/- 0.08 to 0.71 +/- 0.15 at 90 min, respectively. The energy charge of the liver decreased significantly 90 min after 200 micrograms/kg GH injection from 0.872 +/- 0.003 to 0.836 +/- 0.012 (p < 0.05). These results suggest that GH is associated with the deterioration of the hepatic energy metabolism, and that the administration of GH should be carefully weighed up in cases of damaged liver.