OVARIECTOMY FAILS TO MODIFY THE CARDIAC MYOSIN ISOENZYME PROFILE OF ADULT RATS

Estrogen has been shown to help maintain the elevated expression of th e high ATPase myosin isoform, V1, present in the hearts of young rats (< 70 days of age). Because hearts of this age are still undergoing si gnificant maturation, the current study sought to determine if estroge n similarly regulates myosin isoenzyme expression in the mature adult heart. To make this determination, ten month old retired female Spragu e-Dawley rats were made estrogen-deficient by ovariectomy (OVAR, n = 8 ). Sham-operated (CONTR, n = 8) animals served as controls. Nine weeks later, the animals were sacrificed and left ventricular tissue collec ted. Crude myofibrills were isolated from these samples and electropho retically separated into the three isoenzymatic forms of cardiac myosi n (V1, V2, and V3). OVAR animals were larger than the CONTR group (p < 0.05), but heart weight/body weight ratios were not different between groups. Distribution of myosin among its three isoenzymes was similar between groups (CONTR: V1, 80%, V2, 14%; V3, 6%; OVAR: V1, 77%, V2, 1 6%, V3, 7%). These data demonstrate that myosin isoenzyme distribution in the adult heart is unaltered by ovariectomy, suggesting that estro gen loses its ability to regulate expression of this protein in the ma ture heart.