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Departments of 1 Anaesthesia2 Hepatology3 Growth and Reproduction4 Infectious Diseases, The Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark5 Department of Clinical Biochemistry, Bispebjerg Hospital, Copenhagen, Denmark6 Department of Medical Physiology, The Panum Institute, University of Copenhagen, Denmark
Strenuous exercise increases the cerebral uptake of carbohydrate out of proportion to that of oxygen, but it is unknown whether such enhanced carbohydrate uptake is influenced by the marked endocrine response to exercise. During exhaustive exercise this study evaluated the a–v differences across the brain (a–v diff) of hormones that could influence its carbohydrate uptake (n= 9). In addition, neuroendocrine activity and a potential uptake of hormones via the cerebrospinal fluid (CSF) were assessed by lumbar puncture postexercise and at rest (n= 6). Exercise increased the arterial concentration of noradrenaline and adrenaline, but there was no cerebral uptake. However, following exercise CSF noradrenaline was 1.4 (0.73–5.5) nmol l–1, and higher than at rest, 0.3 (0.19–1.84) nmol l–1 (P < 0.05), whereas adrenaline could not be detected. Exercise increased both the arterial concentration of NH4+ and its a–v diff, which increased from 1 (–12 to 5) to 17 (5–41) µmol l–1 (P < 0.05), while the CSF NH4+ was reduced to 7 (0–10) versus 11 (7–16) µmol l–1 (P < 0.05). There was no release from, or accumulation in the brain of interleukin (IL)-6, tumour necrosis factor (TNF-
), heatshock protein (HSP72), insulin, or insulin-like growth factor (IGF)-I. The findings indicate that for maximal exercise, the concentration of noradrenaline is increased within the brain, whereas blood borne hormones and cytokines are seemingly unimportant. The results support the notion that the exercise-induced changes in brain metabolism are controlled by factors intrinsic to the brain.
(Received 13 November 2003;
accepted after revision 30 January 2004; first published online 17 February 2004)
Corresponding author M. K. Dalsgaard: Department of Anaesthesia, Rigshospitalet 2041, Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark. Email: madskd{at}tiscali.dk
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