Received November 13, 2003
Revised January 20, 2004
Accepted after revision January 30, 2004

¹ Rigshospitalet, University of Copenhagen
² Department of Medical Physiology, University of Copenhagen
³ Bispebjerg Hospital, University of Copenhagen

^* To whom correspondence should be addressed. E-mail: madskd{at}tiscali.dk.

	Abstract

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 arterial-venous 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 post-exercise 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 - 5) to 17 (5 - 41) mmol l^-1 (P < 0.05), while the CSF NH₄⁺ was reduced to 7 (0-10) vs. 11 (7-16) mmol 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.

Key Words: Brain, Exercise, Hormones

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