An 18Fluoro-Deoxyglucose Positron Emission Tomography Study
The effect of basal insulin on global and regional brain glucose uptake and metabolism in humans was studied using 18-fluorodeoxyglucose and positron emission tomography (FDG-PET). Eight healthy male volunteers aged 49.3 ± 5.1 years were studied twice in random order. On each occasion, they received an infusion of 0.1 mg · kg−1 · min−1 somatostatin to suppress endogenous insulin production. In one study 0.3 mU · kg−1 · min−1 insulin was infused to replace basal circulating insulin levels, and in the other study a saline infusion was used as control. We sought stimulatory effects of basal insulin on brain glucose metabolism particularly in regions with deficiencies in the blood-brain barrier and high density of insulin receptors. Insulin levels were 27.07 ± 1.3 mU/l with insulin replacement and 3.51 ± 0.4 mU/l without (P = 0.001). Mean global rate of brain glucose utilization was 0.215 ± 0.030 mmol · kg−1 · min−1 without insulin and 0.245 ± 0.021 mmol · kg−1 · min−1 with insulin (P = 0.008, an average difference of 15.3 ± 12.5%). Regional analysis using statistical parametric mapping showed that the effect of basal insulin was significantly less in the cerebellum (Z = 5.53, corrected P = 0.031). We conclude that basal insulin has a role in regulating global brain glucose uptake in humans, mostly marked in cortical areas.
Address correspondence and reprint requests to Dr. Emma Bingham, GKT School of Medicine, King’s College Hospital, London SE5 9PJ, U.K. E-mail:.
Received for publication 19 March 2002 and accepted in revised form 28 August 2002.
CSF, cerebrospinal fluid; CV, coefficient of variation; FDG, 18-fluorodeoxyglucose; LC, lumped constant; MRI, magnetic resonance image; PET, positron emission tomography; SPM, statistical parametric mapping; ROI, region of interest.