Simultaneous NMR microdialysis study of brain glucose metabolism in relation to fasting or exercise in the rat

Abstract

To study the impact of exercise or fasting and of subsequent glucose supplementation on glucose metabolism in rats, a spectrophotometric method was used to determine peripheral blood glucose; a technique associating 1H-NMR spectroscopy and cortical microdialysis was also used to observe intra- plus extracellular and extracellular brain glucose variations, respectively. Compared with control animals (204 ± 19 μM in dialysate, n = 10), exercise increased brain extracellular glucose levels to 274 ± 22 μM ( n = 8; P < 0.05), whereas fasting induced a drop in glucose levels down to 140 ± 9 μM ( n = 8; P < 0.05). After fasting, glucose supplemented by infusion increased glycemia from 7.4 ± 0.4 to 19.9 ± 0.8 mM ( n = 10; P < 0.001), as well as extracellular and extra- plus intracellular brain glucose to 263 ± 20% ( n = 8; P < 0.001) and 342 ± 28% ( n = 8; P < 0.001), respectively, over basal for that group. After exercise, a similar infusion increased glycemia from 7.3 ± 0.3 to 16.8 ± 1.1 mM ( n = 10; P < 0.001), as well as extracellular and extra- plus intracellular brain glucose to 178 ± 19% ( n = 8; P < 0.001) and 244 ± 20% ( n = 8; P < 0.001), respectively, over basal for that group. These results confirmed the existence of a link between glucose level variations in peripheral and cerebral areas but also showed that exercise increased extracellular brain glucose levels despite peripheral hypoglycemia, suggesting a specific regulation mechanism of cerebral glucose metabolism during exercise.