An oral glucose tolerance test does not affect cerebral blood flow: role of NOS

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 325; no. 6; pp. R759 - R768
• Main Authors: Carter, Katrina J., Ward, Aaron T., Al-Subu, Awni, Wilson, Allen D., Zevin, Erika L., Serlin, Ronald C., Eldridge, Marlowe, Wieben, Oliver, Schrage, William G.
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.12.2023
• Series: Don’t Deny Your Inner Environmental Physiologist: Investigating Physiology with Environmental Stimuli
• Subjects: Adult; Adults; Animals; Arginine; Arteries; Blood flow; Cerebral blood flow; Cerebrovascular Circulation; Enzyme Inhibitors - pharmacology; Glucose; Glucose - metabolism; Glucose tolerance; Glucose Tolerance Test; Humans; Hypotheses; Insulin; Insulin - pharmacology; Insulin resistance; Magnetic resonance imaging; Medical imaging; Microvasculature; Monomethyl-L-arginine; Neuroimaging; Nitric oxide; Nitric Oxide Synthase; omega-N-Methylarginine - pharmacology; Perfusion; Placebos; Single-Blind Method; Spin labeling; Vasodilation; cerebral blood flow; healthy adults; OGTT; arterial spin labeling; 4-D flow MRI
• ISSN: 0363-6119; 1522-1490; 1522-1490
• DOI: 10.1152/ajpregu.00169.2022

Animal data indicate that insulin triggers a robust nitric oxide synthase (NOS)-mediated dilation in cerebral arteries similar to the peripheral tissue vasodilation observed in healthy adults. Insulin’s role in regulating cerebral blood flow (CBF) in humans remains unclear but may be important for understanding the links between insulin resistance, diminished CBF, and poor brain health outcomes. We tested the hypothesis that an oral glucose challenge (oral glucose tolerance test, OGTT), which increases systemic insulin and glucose, would acutely increase CBF in healthy adults due to NOS-mediated vasodilation, and that changes in CBF would be greater in anterior regions where NOS expression or activity may be greater. In a randomized, single-blind approach, 18 young healthy adults (24 ± 5 yr) underwent magnetic resonance imaging (MRI) with a placebo before and after an OGTT (75 g glucose), and 11 of these adults also completed an N G -monomethyl-l-arginine (l-NMMA) visit. Four-dimensional (4-D) flow MRI quantified macrovascular CBF and arterial spin labeling (ASL) quantified microvascular perfusion. Subjects completed baseline imaging with a placebo (or l-NMMA), then consumed an OGTT followed by MRI scans and blood sampling every 10–15 min for 90 min. Contrary to our hypothesis, total CBF ( P = 0.17) and global perfusion ( P > 0.05) did not change at any time point up to 60 min after the OGTT, and no regional changes were detected. l-NMMA did not mediate any effect of OGTT on CBF. These data suggest that insulin-glucose challenge does not acutely alter CBF in healthy adults.