UC Irvine

Heart disease is the leading cause of death in the U.S. Premenopausal women generally have lower cardiovascular disease (CVD) rates compared to men, but after menopause, their risk exceeds that of men, largely due to decreased estrogen and progesterone levels. The exact effects of these hormones on cardiac function are still unclear. Our study examined the impact of the estrous cycle on cardiac function in C57BL/6 female mice to gain insights relevant to premenopausal women’s heart health. To access the estrous cycle, we compared two protocols: visual assessment and vaginal cytology and found that vaginal cytology, being more quantitative and less biased, was to be the more reliable method. Among staining protocols, the droplet staining method effectively distinguished cell types and assessed estrous phases. For evaluating cardiac function, a protocol created and implemented for daily transthoracic echocardiography. This included methods for measuring left ventricle wall thickness, internal dimensions, ejection fraction, fractional shortening, and so much more. It was found that while heart rate remained stable throughout the cycle, stroke volume was higher in metestrus and diestrus phases, though not significantly. Notably, fractional shortening and ejection fraction were significantly lower when in diestrus compared to proestrus. This study underscores the importance of considering hormonal phase data in cardiovascular research.