The effect of acute and prolonged endurance exercise on transforming growth factor-ß1 generation in rat skeletal and heart muscle
The serum level of the transforming growth factor-beta1 (TGF-ß1) is elevated after acute bouts of exercise and prolonged training, as well as after myocardial infarction. However, the source of this increase remains unclear. Contracting skeletal muscles are known to be the source of many cytokines. To determine whether skeletal or heart muscles produce TGF-ß1 during exercise, we investigated the effect of a single bout of acute exercise on TGF-ß1 generation in skeletal and heart muscles in untrained rats (UT, n=30) and in rats subjected to prolonged (6-week) endurance training (T, n=29). The UT and T (a day after final training) groups were subjected to an acute bout of exercise with the same work load. Rats from both groups were sacrificed and skeletal and heart muscle samples were collected before (pre), immediately after (0 h), or 3 hours (3 h) after acute exercise. TGF-ß1 mRNA was quantified by RT-PCR in these samples, and basal TGF-ß1 protein levels were determined in skeletal muscle in the UTpre and Tpre subgroups by ELISA. Acute exercise caused a non-significant increase in TGF-ß1 mRNA in skeletal muscle in UT0h rats, in compare to UTpre rats. There was a significant decrease of TGF-ß1 mRNA in the T0h group (p=0.0013) in compare to Tpre rats. Prolonged training caused a significant increase in TGF-ß1 mRNA (p=0.02); however, the TGF-ß1 protein level decreased (p=0.02). In heart muscle, there was a significant decrease of TGF-ß1 mRNA in UT0h (p=0.01) and UT3h (p=0.04) compared to UTpre rats. TGF-ß1 mRNA levels were unchanged in T0h and T3h compared to Tpre; basal TGF-ß1 mRNA expression after training was also unchanged (UTpre vs. Tpre). We conclude that physical exercise is a potent stimulus for inducing TGF-ß1 gene expression in skeletal muscle, but does not increase the protein level. Thus, skeletal and heart muscle do not contribute to increased serum levels of TGF-ß1 after physical exercise.