Estrogen supplement prevents the calcium hypersensitivity of cardiac myofilaments in ovariectomized rats.
Our previous biochemical and mechanical studies have demonstrated an increase in Ca2+ sensitivity of cardiac myofilaments in ovariectomized rats. To test whether the body weight gain associated with ovariectomy contributed some effects to the changes in myofibrillar functions, the relations of pCa (-log Ca2+ molar concentration) to actomyosin adenosine triphosphatase (ATPase) activity of isolated myofibrillar preparations from 10-week pair-fed ovariectomized rats were compared with those from sham-operated controls. Despite similar body weights, the maximum myofibrillar ATPase activity was significantly lower in pair-fed ovariectomized rats as compared to that of sham-operated controls. In addition, the pCa-actomyosin ATPase relationship of pair-fed ovariectomized hearts still demonstrated a significant leftward shift in pCa50 (-log half-maximally Ca2+ activation) from that of sham-operated controls. To find out which hormone was responsible for the observed increase in myofibrillar Ca2+ sensitivity, different sex hormone supplemental regimens were administered to ovariectomized rats. Subcutaneous injection of estrogen (5 microg/rat) or estrogen plus progesterone (1 mg/rat) three times a week could effectively prevent the changes in body weight, heart weight, and uterine weight of the ovariectomized animals. Moreover, supplements of either estrogen or progesterone could prevent a decrease in maximum ATPase activity. In contrast, only the estrogen replacement could abolish the Ca2+ hypersensitivity of the myofilaments in these ovariectomized rats. These results suggest differential cardio-regulatory effects of ovarian sex hormones on the Ca2+ activation of the myofilaments.
Wattanapermpool
J
J
Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand. tejwt@mahidol.ac.th
Riabroy
T
T
Preawnim
S
S
D008841:Actin Cytoskeleton / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001835:Body Weight; D002118:Calcium / Q000378:metabolism*; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D009206:Myocardium / Q000378:metabolism*; D010052:Ovariectomy; D051381:Rats; D017207:Rats, Sprague-Dawley
D004967:Estrogens; D000251:Adenosine Triphosphatases; D002118:Calcium