Cardiovascular pharmacology of hormone replacement therapy

The incidence of cardiovascular disease in women is negligible before natural or surgically-induced menopause, and increases after menopause. Epidemiological data suggest that estrogen replacement therapy reduces the occurrence of coronary artery, and possibly cerebrovascular, disease by 25 to 50% in treated women compared with non-users. These findings are supported by the evidence that estrogens have a beneficial effect on cholesterol metabolism and deposition, contributing to the inhibition of atherosclerotic plaque formation in arterial walls. Early reports suggested that up to 60% of the protective effect of estrogens on coronary artery disease was attributable to favourable changes in plasma lipids. Reanalysis of the data indicated that the lipid changes probably account for approximately 25% of the cardioprotective effect of estrogens and that other effects are, therefore, likely to be important. The influence of estrogens on carbohydrate metabolism, atheroma formation and cardiovascular haemodynamics may also play an integral role in the overall beneficial effect of the hormones. Animal and human studies have shown that the administration of estrogens leads to a restoration of endothelial function, an increase in cardiac output, an increase in arterial flow velocity, a decrease in vascular resistance, and a decrease in systolic and diastolic blood pressure. Recent studies on hormone replacement regimens have shown that estrogens may favourably affect fibrinolysis and reduce plasma fibrinogen to premenopausal levels. Despite these effects of estrogens the recent Heart and Estrogen/Progestin Replacement Study (HERS) failed to show a cardioprotective effect of hormone replacement therapy (HRT) in elderly women with coronary artery disease. However, the HERS study has several limitations and stands alone against the large body of evidence that suggest that HRT may reduce cardiovascular mortality and morbidity.