Estrogen attenuates soleus muscle force decline in female rats after downhill running

Introduction

Unaccustomed exercise, particularly the one involving eccentric contractions, induces skeletal muscle injury. It has been proposed that estrogens have a protective effect on muscle injury, acting as an antioxidant and membrane stabilizer. It is also well documented that functional changes of the muscle following exercise constitute a reliable index of muscle injury. Therefore, the objective of this study was to investigate the role of estrogens on the functional alterations induced by eccentric contraction-biased exercise.

Methods

Forty immature ovariectomized rats were divided into 2 groups. At the age of 9 weeks one group was implanted with 17β-estradiol pellet, which increased the blood estradiol to the levels found in the phase of proestrus, whereas the other group was implanted with placebo pellets. Three weeks after the implantation the rats followed a 90 min intermittent downhill running protocol. Half of the animals of each group were examined immediately after exercise and the other half 72 hours post exercise. Contractile properties of the rat soleus muscle recorded in situ included isometric twitch force (Pt), time-to-peak tension (TPT), half relaxation time (½ RT), as well as tetanic force at stimulation frequencies of 10, 20, 40 and 80 Hz. A fatigue protocol (40 Hz for 3 min) was applied to test for fatigability. A 2 x 2 analysis of variance (2-way ANOVA) was used for statistical analysis.

Results

The results indicated that the estradiol-treated rats improved the soleus muscle contractile properties, compared to the placebo rats. However not all parameters examined were significantly different. The improvement was significant for the unfused tetanic force at 10, 20 and 40 Hz as well as the fatigue index, while Pt, TPT, ½ RT and the fused tetanic force (80 Hz) were non significant.

Discussion/Conclusion

It is suggested that estrogen administration partially counteracts the force decline following eccentric exercise by attenuating the disorganization of the contractile apparatus and the excitation-contraction coupling failure associated with skeletal muscle injury.

References

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