title: Effects of insulin on brain glucose metabolism in impaired glucose tolerance.
abstract: OBJECTIVE
  Insulin stimulates brain glucose metabolism, but this effect of insulin is already maximal at fasting concentrations in healthy subjects. It is not known whether insulin is able to stimulate glucose metabolism above fasting concentrations in patients with impaired glucose tolerance.
  
  
  METHODS
  We studied the effects of insulin on brain glucose metabolism and cerebral blood flow in 13 patients with impaired glucose tolerance and nine healthy subjects using positron emission tomography (PET). All subjects underwent PET with both [(18)F]fluorodeoxyglucose (for brain glucose metabolism) and [(15)O]H(2)O (for cerebral blood flow) in two separate conditions (in the fasting state and during a euglycemic-hyperinsulinemic clamp). Arterial blood samples were acquired during the PET scans to allow fully quantitative modeling.
  
  
  RESULTS
  The hyperinsulinemic clamp increased brain glucose metabolism only in patients with impaired glucose tolerance (whole brain: +18%, P = 0.001) but not in healthy subjects (whole brain: +3.9%, P = 0.373). The hyperinsulinemic clamp did not alter cerebral blood flow in either group.
  
  
  CONCLUSIONS
  We found that insulin stimulates brain glucose metabolism at physiological postprandial levels in patients with impaired glucose tolerance but not in healthy subjects. These results suggest that insulin stimulation of brain glucose metabolism is maximal at fasting concentrations in healthy subjects but not in patients with impaired glucose tolerance.
authors.affiliation: Turku PET Centre, University of Turku and Turku University Hospital, Turku, Finland. jueshi@utu.fi
authors.forename: Jussi
authors.initials: J
authors.lastname: Hirvonen
authors.forename: Kirsi A
authors.initials: KA
authors.lastname: Virtanen
authors.forename: Lauri
authors.initials: L
authors.lastname: Nummenmaa
authors.forename: Jarna C
authors.initials: JC
authors.lastname: Hannukainen
authors.forename: Miikka-Juhani
authors.initials: MJ
authors.lastname: Honka
authors.forename: Marco
authors.initials: M
authors.lastname: Bucci
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Nesterov
authors.forename: Riitta
authors.initials: R
authors.lastname: Parkkola
authors.forename: Juha
authors.initials: J
authors.lastname: Rinne
authors.forename: Patricia
authors.initials: P
authors.lastname: Iozzo
authors.forename: Pirjo
authors.initials: P
authors.lastname: Nuutila
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001823:Body Composition; D001921:Brain / Q000000981:diagnostic imaging / Q000187:drug effects / Q000378:metabolism*; D001931:Brain Mapping; D005260:Female; D005947:Glucose / Q000378:metabolism*; D015309:Glucose Clamp Technique; D018149:Glucose Intolerance / Q000000981:diagnostic imaging / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D011877:Radionuclide Imaging
chemical_list: D007328:Insulin; D005947:Glucose