Effects of Estrogen in the Myocardium of Aged Ovariectomized Rats

ABSTRACT

BACKGROUND AND OBJECTIVES: The effects of estrogen in the myocardium of aged ovariectomized rats, relating to the estrogen replacement onset time following an ovariectomy, and the replacement duration have not yet been established. The object of this study was to investigate the effects of estrogen replacement in the myocardium of aged ovariectomized rats. MATERIALS AND METHODS: 52 Female Sprague Dawley rats, about 3 months old, were subjected to sham surgery only (Group 1 ; control, n=9) ; a bilateral ovariectomy (OVX) and maintained untreated for a period of 12 weeks following surgery (Group 2 ; OVX only, n=16) ; estrogen conjugate 25 microgram/kg daily for 4weeks from the 8th post ovariectomy week (Group 3 ; OVX+estrogen replacement therapy ERT 4weeks, n=10) ; estrogen conjugate 25 microgram/kg daily p.o for 12weeks directly post ovariectomy (Group 4 ; OVX+ERT 12weeks, n=17). We measured the left ventricular wall thickness (LVWT), the number of cardiomyocytes and interstitial fibrosis, edema, using light and electron microscopy. RESULTS: The LVWT in group 4 was 2.25 mm, which was significantly decreased compared to groups 2 and 3, which were 2.45 mm (p=0.014) and 2.46 mm (p=0.008), respectively. The LVWT in group 4 was not significantly different to that of group 1. Interstitial edema was significantly decreased in group 4 (41.2%) compared to that of group 3 (62.0%) (p=0.019). The electron microscopic findings showed a decrease of crystae and a loss of matrix, resulting in a whitish discoloration of the mitochondria in groups 2 and 3. A similar finding was not observed in groups 1 and 4. CONCLUSION: These results suggest that early administration and maintenance of estrogen following a bilateral ovariectomy could prevent the myocardial changes caused by estrogen deficiency.