Rates of Cerebral Glucose Utilization in Rats Anaesthetized With Phenobarbitone

Intraperitoneal injection of phenobarbitone (250 mg/kg body wt.) into rats caused increased brain concentrations of glucose (100 per cent), glucose 6‐phosphate (16 per cent) and ATP (12 per cent) and decreased concentrations of lactate (33 per cent) and ADP (15 per cent). A 31 per cent decrease in glutamate content was not statistically significant. No significant change occurred in the cerebral contents of glycogen or creatine phosphate. The rates of increase in the brain of specific activities, in the first few minutes after systemic injection of [U‐ 14 C]glucose, of glucose, lactate, glutamate and glycogen were all halved by phenobarbitone. Calculated flux rates of 14 C from glucose into metabolic intermediates and from lactate to glutamate were also decreased by 27–47 per cent; the effects on rate constants showed inconsistencies. The rate constants for conversion of glucose to lactate and to glutamate were decreased by 60–70 per cent, but that from lactate to glutamate was virtually unchanged. The rate constant for the flux from glucose to glycogen was reduced by 39 per cent, but the accumulation of glucose meant that the actual flux into glycogen increased by 20 per cent. The results are interpreted in terms of an effect of the barbiturate not only on glucose transport, but also at an enzymic stage in glycolysis, possibly hexokinase or phosphofructokinase.