We have previously reported that the concentration of transforming growth factor- (TGF-) increases in the cerebrospinal fluid of rats during exercise, and that there is an increase in whole-body fat oxidation following the intracisternal administration of TGF-. These results led us to postulate that TGF- in the brain regulates the enhancement of fatty acid oxidation during exercise. To test this hypothesis, we carried out respiratory gas analysis during treadmill running following the inhibition of TGF- activity in rat brain by intracisternal administration of anti-TGF- antibody or SB-431542, an inhibitor of the type 1 TGF- receptor (TR1). We found that each reagent partially blocked the increase in the fatty acid oxidation. We also compared the plasma concentrations of energy substrates in the group administered anti-TGF- antibody and the control group during running. We found that the plasma concentrations of non-esterified fatty acids and ketone bodies in the group administered anti-TGF- antibody were lower than in the control group at the end of running. In the same way, we carried out respiratory gas analysis during treadmill running after depressing CRF activity in the brain using intracisternal administration of astressin, an inhibitor of the CRF receptor. However, there were no significant differences in RER or oxygen consumption in moderate running (60% maximum oxygen consumption). These results suggest that brain TGF- has a role in enhancing fatty acid oxidation during endurance exercise, and that this regulation is executed at least partly via the TR1 signal transduction system.