Effect of endurance training on oestrogen receptor alpha transcripts in rat skeletal muscle

Endurance training induces, in female rats, alterations of oestrous cycle with decrease in plasma oestradiol levels. Moreover, it is well known that oestradiol concentrations modify oestrogen receptor levels. In order to further explain the effects of oestrogens on skeletal muscles, we hypothesized that endurance training modifies the levels of oestrogen receptor alpha messenger ribonucleic acid (ER alpha mRNA) in rat gastrocnemius muscle. Wistar rats were separated into four groups: male controls (C(m)) (n=7), female controls (C(f)) (n=6), male trained (E(m)) (n=7) and female trained (E(f)) (n=6). The endurance training programme was performed for 7 weeks, 5 days week-1 and consisted of 1 h of continuous running on an adapted motor-driven treadmill. At the end of the training session, the gastrocnemius muscle was isolated, weighed and semiquantification of ER alpha mRNA was performed using the reverse transcriptase-polymerase chain reaction (RT-PCR) technique. The citrate synthase (CS) activity of the gastrocnemius muscle was measured by a fluorimetric method. The CS activity of the male and female gastrocnemius muscle, respectively, 100 +/- 7% in C(m) (n=7) vs. 120 +/- 14% in E(m) (n=6, P < 0.01) and 100 +/- 13% in C(f) (n=6) vs. 138 +/- 23% in E(f) (n=6, P < 0.01) was significantly increased after 7 weeks of training. The ER alpha mRNA levels were significantly increased in E(f) compared with C(f) (0.49 +/- 0.15 vs. 0.31 +/- 0.11, P < 0.01) but not in E(m) compared with C(m) (0.37 +/- 0.15 vs. 0.37 +/- 0.13). In conclusion, these results demonstrate that 7 weeks of endurance training increased the level of transcripts encoding ER alpha in rats with the increase restricted to the females.