Using 7.0 T cardiac magnetic resonance to investigate the effect of estradiol on biventricular structure and function of ovariectomized rats exposed to chronic hypobaric hypoxia at high altitude

Despite that estradiol can reduce the risk of cardiovascular diseases in ovariectomized animals in the plains, its effect on animals at high altitude has seldom been reported. We hypothesize that estradiol can ameliorate cardiac damage to ovariectomized rats induced by chronic exposure to hypobaric hypoxia at high altitude. This study was intended to investigate whether cardiovascular magnetic resonance (CMR) imaging could reveal cardioprotective effect of estradiol on ovariectomized rats under chronic exposure to hypobaric hypoxia at high altitude. Thirty-two rats were randomized into the Control group (Plain), HH + Sham group (Hypobaric Hypoxia + Sham), HH + OVX group (Hypobaric Hypoxia + Bilateral Ovariectomy) and HH-OVX + E2 group (Hypobaric Hypoxia + Bilateral Ovariectomy + Estradiol, 50 μg/kg, 3 times a week, for 6 weeks) (n = 8 per group). Except the Control group (altitude: 500 m), rats in other groups were subcutaneously injected with 17β -estradiol or vehicle and exposed to chronic hypobaric hypoxia in Qinghai-Tibet Plateau (altitude: 4250 m), China, for 6 weeks. Biventricular cardiac function and global strain of the rats were measured by CMR and analyzed using the cine tissue tracking techniques. Biochemical tests, histopathology and electronic microscopy were used to evaluate the protective effect of estradiol on the heart tissue of ovariectomized rats exposed to a high-altitude environment. The biventricular ejection fraction and global strains decreased in the HH + OVX group compared with that in the Control group (all p  < 0.05). All the aforementioned changes in the HH + OVX group ameliorated in the HH-OVX + E2 group (all p  < 0.05). Estradiol also alleviated the right ventricular dilatation and hypertrophy in the HH + OVX group (all p  < 0.05). In addition, histological and biochemical analyses also supported these in vivo results. Estradiol ameliorated the biventricular structural and functional damage in ovariectomized rats exposed to chronic hypobaric hypoxia at high altitude.