Evidence of a role of endogenous estrogen in the modulation of autonomic nervous system

The role of ovarian hormones, mainly estrogen, in the modulation of autonomic nervous control of the cardiovascular system is poorly understood. Menopause is associated with an altered control of the cardiovascular system with a shift toward increased sympathetic activity. Natural menopause, however, is the consequence of a process of ovarian senescence and of a slow but gradual decrease in plasma levels of ovarian hormones. To evaluate the physiologic role of estradiol-17β in the modulation of the nervous autonomic control of the cardiovascular system, we evaluated the effect of acute withdrawal of ovarian hormones on the balance of vagal and sympathetic influences on the cardiovascular system. For this purpose analysis of heart rate variability (HRV) was performed on the 24-hour electrocardiographic recordings of a group of fertile women at basal conditions and during the 5 weeks immediately subsequent to bilateral oophorectomy. Data obtained were compared with those from a group of age-matched women who had undergone hysterectomy with conservation of the ovaries. Observations were repeated in oophorectomized persons after 3 months of estrogen replacement therapy (ERT).