Search

Hypertrophy of liver cells, as measured by decreased mg DNA per g wet liver, from obese mice (C57BL/6J ob/ob) was associated with a marked increase in triacylglycerol content per g wet liver when compared with control lean mice (C57BL/6J ?/+). The difference between the rates of net glucose production from lactate in isolated perfused livers from obese and lean mice was small when expressed per g wet liver. However, calculation of these rates either on a DNA or body weight basis indicated that the rate of gluconeogenesis in livers from obese mice was twice that of lean mice. Using perfused livers from lean mice, the ratio of net uptake of C3-substrate to gluconeogenesis indicated that a major proportion of lactate disappearing from the perfusion medium could not be accounted for in the appearance of glucose; but using the perfused livers of obese mice, almost all of the net lactate disappearance could be accounted for by a net increase in glucose production.

Chronic treatment of rats with dithiobiuret (DTB) produces a delayed onset muscle weakness and, as suggested by a preliminary study, a distal axonopathy. An inhibition of glycolysis resulting in an energy deficit has been suggested as a possible mechanism of neurotoxin-induced distal axonopathies. To determine whether chronic DTB administration (1 mg/kg/day X 7 days; sacrificed on Day 7) might be associated with a perturbation of glucose metabolism in neuronal tissues, lactate production was measured in brain and spinal cord homogenates prepared from rats which exhibited hindlimb skeletal muscle weakness. Kinetic and statistical analysis showed that glucose-dependent lactate production in these homogenates was not different from that of controls. Lactate production was also determined in brain homogenates prepared from rats intoxicated with acrylamide (50 mg/kg/day X 9 days; sacrificed on Day 9), p-bromophenylacetylurea (200 mg/kg/day X 2 days; sacrificed on Day 14) or 2,5-hexanedione (400 mg/kg/day X 21 days; sacrificed on Day 21). The results indicated that whereas 2,5-hexanedione produced a slight decrease in Vmax, acrylamide and p-bromophenylacetylurea did not cause changes in glucose-dependent lactate production. These findings do not support the suggestion that an inhibition of glycolysis represents a common biochemical lesion associated with neurotoxins which cause delayed onset muscle weakness and distal axonopathy.

Livers of fasted rats were perfused for 70 min at 37 degrees-43 degrees C in the presence or absence of acetate, octanoate or palmitate. Hepatic biosynthetic capacity was assessed by measuring rates of gluconeogenesis, ureogenesis, ketogenesis and O2 consumption. In the presence of each fatty acid, gluconeogenesis, ureogenesis and oxygen consumption were maintained at 37 degrees and 42 degrees C. At 43 degrees, the rate of glucose formation decreased markedly and rates of ureogenesis and oxygen consumption were distinctly lower. As the temperature was increased from 37 degrees to 43 degrees C without fatty acids, i.e. albumin only, there was a progressive decrease in the rate of gluconeogenesis while the ratio of net C3 utilized to glucose formed, increased successively. The values of this ratio in the presence of palmitate or octanoate at 43 degrees were smaller than those for albumin or acetate, but higher than the figure of 2 for complete conversion of C3 units to glucose. Although fatty acid was added in equimolar amounts of C2 units, total ketone formation was influenced significantly by chain length. Hepatic ketogenesis was similar at 37 degrees with albumin, palmitate, or acetate, but was stimulated significantly by octanoate at 37 degrees and 42 degrees C. At 42 degrees, ketone formation increased in the presence of palmitate. At 43 degrees C, ketogenesis with palmitate or octanoate decreased, while that with acetate or albumin was maintained at the same lower rates. The ratio of 3-hydroxybutyrate to acetoacetate in the perfusate was increased with palmitate at the end of perfusion at 37 degrees and 42 degrees C or octanoate at 42 degrees and 43 degrees C. Thus, long (palmitate)- and medium (octanoate)- but not short (acetate)-chain fatty acids enhance not only beta-oxidation, but influence the redox state of hepatic mitochondria with an increase in the state of reduction of the pyridine nucleotides. Such a shift in the redox state would be operable in the perfused liver even at 43 degrees C and may be responsible for improved conversion of lactate to glucose when medium- or long-chain fatty acids are present at hyperthermic temperatures.