1. ¹Neurobiology Research Unit 9201, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark
2. ²The Danish Research Centre for Magnetic Resonance, Copenhagen University Hospital, Hvidovre, Denmark

Correspondence: Professor OB Paulson, Neurobiology Research Unit 9201, Rigshospitalet, Copenhagen University Hospital, 9 Blegdamsvej, DK-2100 Copenhagen, Denmark. E-mail: paulson@nru.dk

Received 25 February 2005; Revised 4 May 2005; Accepted 25 May 2005; Published online 6 July 2005.

Abstract

In the human setting, it has been shown that acute increase in the concentration of ketone bodies by infusion of -hydroxybutyrate increased the cerebral blood flow (CBF) without affecting the overall cerebral metabolic activity. The mechanism by which this effect of ketone bodies was mediated is not known. Alterations in several parameters may possibly explain the increase in CBF and the resetting of the relation between CBF and cerebral metabolism. To study this phenomenon further, we measured global CBF and global cerebral metabolism with the Kety–Schmidt technique in the wakeful rat before and during infusion of ketone bodies. During acute hyperketonemia (average concentration of -hydroxybutyrate: 6 mmol/L), global CBF increased 65% from 108 to 178 mL/100 g min and the cerebral metabolic rates for both oxygen and glucose remained constant. This resetting of the relation between CBF and cerebral metabolism could not be explained by alterations in blood pH or arterial CO₂ tension. By measuring cerebral intracellular pH by ³¹P nuclear magnetic resonance spectroscopy, it could further be concluded that the brain pH was unchanged during acute hyperketonemia. These observations indicate that the mechanism responsible for the increase in CBF is rather a direct effect on the cerebral endothelium than via some metabolic interactions.