The Effect of Insulin Infusion on the Metabolites in Cerebral Tissues Assessed With Proton Magnetic Resonance Spectroscopy in Young Healthy Subjects With High and Low Insulin Sensitivity

OBJECTIVE: Insulin may play important roles in brain metabolism. Proton magnetic resonance spectroscopy ((1)H-MRS) of the central nervous system gives information on neuronal viability, cellular energy, and membrane status. To elucidate the specific role of insulin action in the brain, we estimated neurometabolites with (1)H-MRS and assessed their regulation by insulin infusion and their relationship with insulin sensitivity. RESEARCH DESIGN AND METHODS: We studied 16 healthy young men. (1)H-MRS was performed at baseline and after 240 min of euglycemic-hyperinsulinemic clamp. Voxels were positioned in the left frontal lobe, left temporal lobe, and left thalamus. The ratios of N-acetylaspartate (NAA), choline-containing compounds (Cho), myo-inositol, and glutamate/glutamine/γ-aminobutyric acid complex (Glx) to creatine (Cr) and nonsuppressed water signal were determined. The participants were divided into subgroups of high (high IS) and low (low IS) insulin sensitivity. RESULTS: Baseline neurometabolic substrates were not different between the groups. Insulin infusion resulted in an increase in frontal NAA/Cr and NAA/H(2)O and frontal and temporal Glx/Cr and Glx/H(2)O and a decrease in frontal Cho/Cr and temporal Cho/H(2)O and myo-inositol/H(2)O (all P < 0.05, except temporal Glx/H(2)O, P = 0.054, NS) in the high-IS, but not in the low-IS, group. Insulin sensitivity correlated positively with frontal NAA/Cr and NAA/H(2)O and temporal Glx/H(2)O and negatively with temporal myo-inositol/Cr and myo-inositol/H(2)O assessed during the second (1)H-MRS (all P < 0.05). CONCLUSIONS: Insulin might influence cerebral metabolites, and this action is impaired in subjects with low whole-body insulin sensitivity. Thus, our results provide a potential link between insulin resistance and altered metabolism of the central nervous system.