Carbohydrate metabolism in the brain of the adult lamprey

Abstract

Abstract Carbohydrate metabolism was examined in brain pieces isolated from spawning (anadromous, New Brunswick, N.B.) and prespawning upstream migrant (landlocked, Toronto) lampreys ( Petromyzon marinus ). Brain glycogen concentration in the N.B. lampreys was 2.61 μmol mg −1 protein or 286 μmol g −1 tissue wet wt., significantly above that in the Toronto group (0.34 μmol mg −1 protein; 37 μmol g −1 tissue wet wt.). When glucose was added to an incubate of brain pieces, there was no change in glucose concentration, except in the presence of 10 −7 M insulin, which resulted in net glucose uptake by the tissue. Glucose was metabolized by the brain pieces to both glycogen and CO 2 , with 12% (N.B.) and 32% (Toronto) of the glucose converted to glycogen. Insulin significantly increased glucose flux to glycogen, and epinephrine increased glucose flux to both CO 2 and glycogen. Total lactate utilization by the brain pieces was greater than glucose utilization. Although only 2% of the utilized lactate was converted to glycogen, glycogen synthesis from lactate was 25–30% of glycogen synthesis from glucose. PEPCK activities were found in the brain, indicating the potential for a traditional gluconeogenic pathway. This study supports the hypothesis that gluconeogenesis from C 3 substrates can contribute to brain glycogen synthesis in adult lamprey. © 1993 Wiley‐Liss, Inc.