Caffeine inhibits exercise-induced increase in tryptophan hydroxylase expression in dorsal and median raphe of Sprague-Dawley rats

Effect of caffeine on the expression of tryptophan hydroxylase (TPH), rate limiting enzyme of serotonin synthesis, in dorsal and median raphe was inve stigated via immunohistochemistry. In exercise groups, Sprague-Dawley rats were put on treadmill running for 30 min per day for 6 consecutive days. On the seventh day, animals of control-with-caffeine group were injected subc utaneously with 4 mg/kg caffeine, while control-without-caffeine group were injected with 0.9% NaCl, sacrificed 2 h later. Exercise-with-caffeine grou p and exercise-without-caffeine group were injected with caffeine and NaCl, respectively; all-out time was determined 1 h after injection, and then sa crificed. Caffeine increased all-out time in exercised rats, and inhibited the exercise-induced elevation in TPH expression. The suppressive effect of caffeine on TPH expression in exercised rats can be suggested as one possi ble ergogenic mechanism of caffeine. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.