Received June 28, 2004
Revised August 3, 2004
Accepted after revision September 21, 2004
Effect of Estrogen on Myofibre Size and Myosin Expression in Growing Rats
Christy M. Piccone 1,
Gayle A. Brazeau 1,
Kathleen M. McCormick 1*
1 University at Buffalo
* To whom correspondence should be addressed. E-mail: kmccorm{at}buffalo.edu.
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Abstract |
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This study examined the effect of estrogen deprivation and replacement on plantaris muscle size and myosin heavy chain (MHC) isoform composition in rats during a period of physiological growth. Seven week old female Sprague-Dawley rats were assigned to one of the three treatment groups: 1) control animals (SHAM), 2) ovariectomized animals without estrogen replacement (OVX/CO), and 3) ovariectomized animals with 17 
-estradiol replacement (OVX/E2). OVX/CO and OVX/E2 animals were pair-fed to SHAM animals to rule out the potentially confounding effects of differences in food intake and weight gain. Rats were sacrificed four weeks after surgery and the plantaris muscle was removed for analysis. Ovariectomy had no effect on muscle fibre size, but reduced the relative amount of type IIx MHC. This was reversed with estrogen replacement suggesting that the reduction in type IIx MHC expression was an estrogen-mediated effect. Estrogen replacement reduced type IIb MHC expression and fast muscle fibre size. Changes in fast fibre size and IIb MHC expression were not seen with ovariectomy, indicating that these changes were not simply due to the presence of estrogen in the estrogen replaced animals. These results suggest that another ovarian hormone counteracts the effect of estrogen on fast fibre size and IIb MHC expression in intact animals.
Key Words:
Myosin, Oestrogen, Skeletal muscle
