ABSTRACT
This study examined the effect of oestrogen 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 oestrogen replacement (OVX/CO); and (3) ovariectomized animals with 17beta-oestradiol replacement (OVX/E2). OVX/CO and OVX/E2 animals were pair-fed with Sham animals to rule out the potentially confounding effects of differences in food intake and weight gain. Rats were killed 4 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 oestrogen replacement, suggesting that the reduction in type IIx MHC expression was an oestrogen-mediated effect. Oestrogen replacement reduced type IIb MHC expression and fast muscle fibre size. Changes in fast fibre size and type IIb MHC expression were not seen with ovariectomy, indicating that these changes were not simply due to the presence of oestrogen in the ovariectomized, oestrogen-replaced animals. These results suggest that another ovarian hormone may counteract the effect of oestrogen on fast fibre size and type IIb MHC expression in intact animals.
Subject(s)
Aging/physiology , Estradiol/administration & dosage , Hormone Replacement Therapy/methods , Muscle Fibers, Skeletal/metabolism , Muscle Fibers, Skeletal/pathology , Myosin Heavy Chains/metabolism , Myosins/metabolism , Animals , Gene Expression Regulation, Developmental/drug effects , Gene Expression Regulation, Developmental/physiology , Muscle Fibers, Skeletal/drug effects , Muscle, Skeletal/drug effects , Muscle, Skeletal/metabolism , Muscle, Skeletal/pathology , Organ Size/drug effects , Ovariectomy , Rats , Rats, Sprague-DawleyABSTRACT
This study examined the effect of estrogen replacement on soleus muscle size and contractile function in ovariectomized rats during physiological growth. Seven week old female Sprague-Dawley rats were assigned to one of three treatment groups: (1) control animals (SHAM), (2) ovariectomized animals without estrogen replacement (OVX/CO), and (3) ovariectomized animals with 17 beta-estradiol replacement (OVX/E2). OVX/CO and OVX/E2 animals were pair-fed to SHAM animals to rule out the potentially confounding effect of differences in food intake. Rats were sacrificed 4 weeks after surgery and the soleus muscle was removed for analysis. Estrogen replacement reduced body weight, relative body weight gain, and soleus muscle fiber size despite all groups having a similar food intake. Ovariectomy alone had no effect on any of these parameters suggesting that estrogen may inhibit skeletal muscle growth when it is the only ovarian hormone present. Neither ovariectomy nor estrogen replacement affected maximal specific isometric force. Estrogen replacement increased half relaxation time. Ovariectomy resulted in a reduction in time to peak tension that was reversed with estrogen replacement. This reduction was not accompanied by a change in myosin heavy chain composition implying that calcium handling may have been altered. Results from this study suggest that estrogen affects skeletal muscle growth and twitch kinetics.
