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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Transforming growth factor- in the brain is activated by exercise and increases mobilization of fat-related energy substrates in rats

¹Laboratory of Nutrition Chemistry, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kyoto; and ²Laboratories of Food Science and Nutrition, Department of Life Style Studies, School of Human Cultures, The University of Shiga Prefecture, Shiga, Japan

Submitted 4 September 2006 ; accepted in final form 12 February 2007

We have recently reported that inhibition of transforming growth factor (TGF)- in the brain reduced fat-related energy substrates concentrations in response to exercise. We investigated the relevance between the mobilization of fat-related energy substrates (nonesterified fatty acid and ketone bodies) during exercise and the effects of TGF- in the brain. Low-intensity exercise was simulated by contraction of the hindlimbs, induced by electrical stimulation at 2 Hz in anesthetized rats (Sim-Ex). As with actual exercise, it was confirmed that mobilization of carbohydrate-related energy substrates (glucose and lactic acid) occurred immediately after the onset of Sim-Ex, and mobilization of fat-related energy substrates followed thereafter. The timing of mobilization of fat-related substrates corresponded to that of the increase in TGF- in cerebrospinal fluid (CSF) in Sim-Ex. The level of TGF- in CSF significantly increased after 10 min of Sim-Ex and remained elevated until 30 min of Sim-Ex. Intracisternal administration of TGF- caused rapid mobilization of fat-related energy substrates. Meanwhile, there were no effects on the changes in carbohydrate-related substrates. The levels of catecholamines were slightly elevated after TGF- administration, and, although not significantly in statistical terms, we consider that at least a part of TGF- signal was transducted via the sympathetic nervous system because of these increases. These data indicate that TGF- in the brain is closely related to the mobilization of fat-related energy substrates during low-intensity exercise. We hypothesized that the central nervous system plays a role in the regulation of energy metabolism during low-intensity exercise and this may be mediated by TGF-.

central nervous system; energy metabolism; flux; ketone bodies; nonesterifed fatty acid