Low cerebral glucose extraction rates in the human medial temporal cortex and cerebellum

Previous studies have reported that there exist different regional sensitivities to acute hypoxia. To better understand these differences, we estimated regional differences of cerebral blood flow (CBF), cerebral glucose metabolism (CMRglc) and kinetic constants (K(1), k(2), k(3)) in the human cortex under resting conditions. CBF, CMRglc, kinetic rate constants and glucose extraction rate (GER) were measured in eight normal male subjects (mean age: 26.1+/- 4.9 years) using the 15O-water autoradiographic technique and subsequently the dynamic and the static [18F]2-fluoro-2-deoxy-D-glucose technique with positron emission tomography (PET). Of all the brain structures investigated, the medial temporal lobe showed the lowest CBF (46.0 ml/100 g/min) and lowest CMRglc (3.97 mg/100 g/min). The medial temporal GER was lowest (8.9%), followed by the cerebellar GER (9.3%). While the cerebellar blood flow (64.0 ml/100 g/min) was the highest, the cerebellar metabolic rate for glucose (5.79 mg/100 g/min) was relatively low. The cerebellum showed the highest K(1) value (0.13) and k(2) value (0.16), and the lowest k(3) value (0.05). In the medial temporal cortices and cerebellum, CMRglc and GER were lower than those in the neocortices. These results indicate that there are great perfusional/metabolic differences between the medial temporal lobe, cerebellum and other brain regions in the normal human brain under resting conditions.