EFFECTS OF PROLONGED EXERCISE ON BRAIN AMMONIA AND AMINO-ACIDS

The aim of this study was to investigate if enhanced peripheral ammoni a production during exhaustive exercise increases ammonia detoxication in brain mediated by glutamine synthesis, and subsequently influences glutamate and gamma-aminobutyric acid (GABA) levels. This neurotransm itter production is related to the metabolism of glutamine, A group of rats was trained for 6 weeks by treadmill running (TR). They were com pared to a group of untrained rats (UN). At the end of training, half of TR and UN rats were submitted to one session of treadmill running u ntil exhaustion (288 +/- 12 min and 62 +/- 5 min in TR and UN group, r espectively). At exhaustion, running and control rats were sacrificed in order to collect blood and to take samples of the following brain s tructures: cortex, striatum and cerebellum. Treadmill running until ex haustion induced an increase in blood ammonia by 140% without signific ant differences between TR and UN groups. Brain ammonia increased in b oth groups. However, TR group exhibited values 50% higher than those o bserved in UN group. Brain glutamine was increased at exhaustion in al l groups of Funning rats by 30-75% of basal value whereas the glutamat e only decreased in TR rats which were able to run for a longer time. In this group, the GABA level decreased in striatum. These data confir m that enhanced brain ammonia level during exercise stimulates glutami ne synthesis as a mechanism of detoxication. After several hours of ru nning, a reduction in brain glutamate levels was observed in all brain structures in trained rats but only in the striatum in untrained anim als. The reduced availability of this GABA precursor decreases GABA le vels only in the striatum of TR group by 45% of the resting value. The se results suggest a relation between cerebral changes in neurotransmi tters and excitatory amino acids, such as glutamate and GABA, and cent ral fatigue.