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Original Studies |
Neurobiology Research Unit, Department of Neurology, and the PET and Cyclotron Unit, University Hospital, Rigshospitalet (S.G.H., G.M.K., O.B.P.), DK-2100 Copenhagen, Denmark; and Institute of Internal Medicine and Metabolic Diseases, Universita Degli Studi Di Napoli Federico II (B.C., A.P.), 80131 Naples, Italy
Address all correspondence and requests for reprints to: Steen G. Hasselbalch, M.D., Neurobiology Research Unit, Building 9201, National University Hospital, Rigshospitalet, 9 Blegdamsvej, DK-2100 Copenhagen Ø, Denmark. E-mail: sgh{at}pet.rh.dk
It is controversial whether transport adaptation takes place in chronic or acute hyperglycemia. Blood-brain barrier glucose permeability and regional brain glucose metabolism (CMRglc) was studied in acute hyperglycemia in six normal human subjects (mean age, 23 yr) using the double indicator method and positron emission tomography and [18F]fluorodeoxyglucose as tracer. The Kety-Schmidt technique was used for measurement of cerebral blood flow (CBF). After 2 h of hyperglycemia (15.7 ± 0.7 mmol/L), the glucose permeability-surface area product from blood to brain remained unchanged (0.050 ± 0.008 vs. 0.059 ± 0.031 mL/100 g·min). The unidirectional clearance of [18F]fluorodeoxyglucose (K1*) was reduced from 0.108 ± 0.011 to 0.061 ± 0.005 mL/100 g·min (P < 0.0004). During hyperglycemia, global CMRglc remained constant (21.4 ± 1.2 vs. 23.1 ± 2.2 µmol/100 g·min, normo- and hyperglycemia, respectively). Except for a significant increase in white matter CMRglc, no regional difference in CMRglc was found. Likewise, CBF remained unchanged.
The reduction in K1* was compatible with Michaelis-Menten kinetics for facilitated transport. Our findings indicate no major adaptational changes in the maximal transport velocity or affinity to the blood-brain barrier glucose transporter. Finally, hyperglycemia did not change global CBF or CMRglc.
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