INDUCTION OF NUCLEAR RESPIRATORY FACTOR-I EXPRESSION BY AN ACUTE BOUTOF EXERCISE IN RAT MUSCLE

Nuclear respiratory factor 1 (NRF-1) is a regulatory factor of nuclear genes for respiratory subunits and for components of the mitochondria l transcription and replication machinery. This study investigated the effects of an acute bout of aerobic exercise on the postexercise expr ession of mRNA for NRF-1 and RNA moiety of endonuclease for mitochondr ial RNA processing (MRP-RNA) in soleus muscle of 5 days-trained and un trained rats. In the trained group, rats were run on a motor-driven tr eadmill at a speed of 25 m/min for 90 min/day for 5 days. On the final day, rats were run by the same procedures and were sacrificed at vari ous postexercise time points (0.5, 3, 6, and 24 h). The basal level of cytochrome oxidase activity was increased by the training, which was associated with the increase in the expression of mRNAs for subunit VI c and III of the enzyme. The NRF-1 mRNA expression was transiently inc reased by similar to 35% at the time point of 6 h after exercise, alth ough the basal level of the expression was not altered by training. A similar transient increase (similar to 50%) in NRF-1 expression by the acute bout of exercise was also observed in untrained rats. In contra st to the NRF-1 expression, the basal level of MRP-RNA abundance was n ot altered by 5 days training and was not affected by the single exerc ise bout in either 5 days-trained or untrained rats. These results sug gest that the postexercise increase in NRF-1 mRNA expression in rat sk eletal muscle may be an early response to endurance exercise for an en hancement of the mitochondrial oxidative capacity. (C) 1998 Elsevier S cience B.V. All rights reserved.