Hexose diphosphates and phosphofructokinase in rat brain during development

Fructose 2,6-diphosphate and glucose 1,6-diphosphate concentrations were determined during late gestation and over the course of suckling in rat brain cortex and cerebellum. Cortex fructose 2,6-diphosphate concentration was greatest in neonatal animals and gradually declined thereafter by 25% to reach the adult level at 15 days of age. In contrast, the glucose 1,6-diphosphate concentration increased 4-fold over the same period to reach its highest level by postnatal day 15. Neither cerebellar fructose 2,6-diphosphate nor glucose 1,6-diphosphate concentrations varied significantly. Six day cortex 6-phosphofructo-1-kinase was less sensitive to inhibition by citrate than the enzyme obtained from 15 day pups, and fructose 2,6-diphosphate was better than glucose 1,6-diphosphate at relieving the inhibition imposed by citrate at either age. It is suggested that the rise in cerebral glucose use which occurs during suckling cannot be attributed to either changes in the concentrations of fructose 2,6-diphosphate or glucose 1,6-diphosphate, or the age-related differential sensitivity of 6-phosphofructo-1-kinase toward these effectors.