Coronary heart disease (CHD) is the leading cause of death in women, and the risk of this disease rises markedly after loss of ovarian function. Hormone replacement therapy (HRT) can reduce the incidence of CHD in postmenopausal women by 50%. HRT causes changes in lipids and lipoproteins, but it is now clear that many other effects of gonadal steroid hormones have important influences on the cardiovascular system. These nonlipid effects include a variety of changes in other metabolic risk factors for CHD, as well as direct arterial effects.
Insulin resistance and hyperinsulinaemia may be pivotal disturbances in the pathogenesis of CHD. Estradiol reverses the effects of menopause on glucose and insulin metabolism, resulting in an increase in pancreatic insulin secretion and a decrease in insulin resistance, although other types of estrogen may not do this. Androgenic progestogens may oppose this potentially beneficial effect on insulin resistance.
Central obesity is linked with many CHD risk factors, and HRT reverses the increased fat distribution that results from loss of ovarian function at the menopause. HRT may also improve the balance between coagulation and fibrinolysis, resulting in a reduction in arterial thrombosis.
Finally, estradiol acts directly on the arterial wall, modifying both endothelium-dependent and calcium-dependent processes. These actions result in improved blood flow and reduced blood pressure and, importantly, have the potential to reduce myocardial ischaemia.