Biochemical aspects of bovine ketosis.

1. The concentrations of acetoacetate, beta-hydroxybutyrate and metabolites related to gluconeogenesis were determined in biopsy samples of the livers of ketotic, normal lactating and normal non-lactating cows. Key enzymes of gluconeogenesis in the liver were also assayed. 2. Significant decreases were found in the ketotic liver in the concentrations of glucogenic amino acids (glutamate, glutamine, alanine) and of glucogenic oxo acids (alpha-oxoglutarate, pyruvate, oxaloacetate). 3. The beta-hydroxybutyrate/acetoacetate concentration ratios were generally much higher than in rat liver. 4. The concentration of total fat was sevenfold higher in the ketotic liver, and that of glucose plus glycogen fourfold lower than in normal liver. 5. The blood of ketotic cows showed a marked rise in the concentration of free fatty acids. 6. The activities of pyruvate carboxylase, propionyl-CoA carboxylase, phosphopyruvate carboxylase and fructose 1,6-diphosphatase showed no clear-cut differences between normal and ketotic animals. 7. Glucose injection promptly relieved the ketotic condition with respect to both the clinical and biochemical signs. The fall in the concentrations of the ketone bodies in the blood was preceded by a fall in the concentrations of free fatty acids and glycerol. 8. The findings are taken to be consistent with the concept that an increased rate of gluconeogenesis, causing a decrease in the concentration of oxaloacetate, is a major causal factor in ketogenesis.