Partitioning and extraction of glucose regulates cerebral glucose utilization in newborn dogs

We investigated the amount of fasting steady-state systemic glucose production utilized by the neonatal canine cerebral cortex. The relationship of systemic glucose production and cerebral glucose utilization were analyzed as functions of cerebral blood flow, cerebral oxygen uptake, and indirect measures of alternate fuel utilization. Fasting arterial blood glucose was 3.36 mM and glucose production was 49.6 mumol/kg/min. Average cerebral blood flow was 0.83 ml/g/min, and cerebral glucose uptake was 0.60 +/- 0.15 mumol/g/min. 36.6% of systemic glucose production was utilized by the cerebral cortex. There were no correlations between systemic glucose production, cerebral blood flow, or cerebral glucose uptake with blood glucose concentration. Furthermore, total cerebral glucose uptake was static across a wide range of glucose levels. Nonetheless, the percent of glucose production used by the brain was an inverse function of systemic glucose production (r = -0.71, p less than 0.001). The cerebral extraction of glucose (27.6 +/- 4.1%) decreased as a function of increasing blood glucose levels (r = -0.51, p less than 0.05), while brain uptake index correlated with increasing systemic glucose production (r = 0.61, p less than 0.02). We can conclude that the canine neonatal cerebral cortex may utilize only 37% of systemic glucose production. At low rates of glucose turnover, a larger proportion of systemic glucose production is allotted to the brain. Mechanisms that may regulate total cerebral glucose influx may be glucose permeability, or the increased extraction of glucose at lower blood glucose levels.