Although it has been demonstrated that exercise training has an antiapoptotic effect on postmitotic myocytes, the mechanisms responsible for this effect are still largely unclear. Because the antiapoptotic effect of exercise training in postmitotic myocytes could be possibly mediated by the upregulation of apoptotic suppressors, this study examined the effect of
endurance training on endogenous apoptotic suppressors including X-chromosome-linked
inhibitor of apoptosis protein (XIAP), apoptosis repressor with
caspases recruitment domain protein (
ARC), and FADD-like inhibitor
protein (FLIP) in skeletal and cardiac muscles. Eight adult Sprague-Dawley rats were trained 5 days weekly for 8 wk on treadmill, and eight sedentary rats served as controls. Soleus and ventricle muscles were dissected 2 days after the last training session. The
mRNA content of XIAP,
ARC, and FLIP was estimated by RT-PCR with ribosomal 18S
RNA used as an internal control. The
protein expression of XIAP,
ARC,
FLIP(S), and FLIP(alpha) was assessed by Western immunoblot. After training,
mRNA content of
ARC and FLIP was not different between the control and trained animals, whereas XIAP
mRNA content was elevated by 22 and 14% in the trained soleus and cardiac muscles, respectively, relative to the control samples. No difference was found in the
protein content of
FLIP(S) and FLIP(alpha) between control and trained muscles, whereas XIAP and
ARC protein content was increased by 18 and 38%, respectively, in the soleus muscle of trained animals. Furthermore, negative relationships were found between XIAP and apoptotic DNA fragmentation as well as
ARC and
caspase-3 activity. These findings are consistent with the hypothesis that the modulation of apoptotic suppressors is involved in training-induced attenuation of apoptosis in skeletal and cardiac muscles.