Local cerebral glucose utilization and blood flow during metabolic acidosis

The relationship between local cerebral glucose utilization (LCGU) and local cerebral blood flow (LCBF) was studied in two groups of normal conscious rats. LCGU was measured by the [14C]deoxyglucose technique and LCBF by the [14C]iodoantipyrine technique. When the LCGU of 39 brain structures was correlated with their respective values of LCBF an excellent correlation (r = 0.96) was obtained between LCGU and LCBF, demonstrating a tight coupling at a local level. Chronic metabolic acidosis was induced in two other groups of rats by adding 0.35 M NH4Cl to the drinking water for 5-6 days. This resulted in a significant (P less than 0.01) reduction in overall cerebral glucose utilization (-29%) and a nonsignificant reduction in overall cerebral blood flow (-8%). This dissociation between the overall cerebral glucose utilization and blood flow during metabolic acidosis cannot be taken as an indicator of uncoupling because the values for LCGU were still well correlated (r = 0.95) with the values for LCBF, indicating a resetting of the coupling mechanism to a new level.