Effect of chronic hypoglycaemia on glucose concentration and glycogen content in rat brain: A localized 13C NMR study.
While chronic hypoglycaemia has been reported to increase unidirectional glucose transport across the blood-brain barrier (BBB) and to increase GLUT1 expression at the endothelium, the effect on steady-state brain d-glucose and brain glycogen content is currently unknown. Brain glucose and glycogen concentrations were directly measured in vivo using localized 13C magnetic resonance spectroscopy (MRS) following 12-14 days of hypoglycaemia. Brain glucose content was significantly increased by 48%, which is consistent with an increase in the maximal glucose transport rate, Tmax, by 58% compared with the sham-treated animals. The localized 13C NMR measurements of brain glucose were directly validated by comparison with biochemically determined brain glucose content after rapid focused microwave fixation (1.4 s at 4 kW). Both in vivo MRS and biochemical measurements implied that brain glycogen content was not affected by chronic hypoglycaemia, consistent with brain glucose being a major factor controlling brain glycogen content. We conclude that the increased glucose transporter expression in chronic hypoglycaemia leads to increased brain glucose content at a given level of glycaemia. Such increased brain glucose concentrations can result in a lowered glycaemic threshold of counter-regulation observed in chronic hypoglycaemia.
Lei
Hongxia
H
Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA.
Gruetter
Rolf
R
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D001812:Blood-Brain Barrier; D001921:Brain / Q000378:metabolism*; D004195:Disease Models, Animal; D005947:Glucose / Q000378:metabolism*; D007003:Hypoglycemia / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D051381:Rats; D012016:Reference Values
D001786:Blood Glucose; D005947:Glucose