Differing effects of low-dose estrogen-progestin therapy and pravastatin in postmenopausal hypercholesterolemic women

Most studies examining the potential cardioprotective effects of postmenopausal estrogen have been undertaken in healthy women, with doses that may not be appropriate for long-term intervention. New low-dose estrogen-progestin regimens alleviate postmenopausal symptoms with a favorable side-effect profile; however, little is known of the impact of such regimens in women at increased risk of cardiovascular disease. Hence, we have evaluated the effects of low-dose oral estrogen-progestin therapy on serum lipoprotein lipids, brachial artery reactivity and fibrinogen in hypercholesterolemic postmenopausal women in direct comparison with the effects of pravastatin, a lipid-lowering agent known to reduce cardiovascular events in women.

In a randomized, double-blind, double-dummy, parallel trial, we studied the effects of continuous combined estrogen-progestin therapy (1 mg 17beta-estradiol with 500 micro g norethisterone acetate daily) or pravastatin (20 mg daily) in 72 postmenopausal women with fasting serum low-density lipoprotein (LDL) cholesterol levels greater than 124 mg/dl after an 8-week run-in diet, over a 24-week period. The primary end-point was percentage change in LDL cholesterol from baseline.

The intention-to-treat population comprised 65 women, mean age 59 +/- 6.3 years, and 29 in each group completed the trial. Diet alone reduced LDL cholesterol significantly in both treatment groups, in association with a reduction in weight during this period. Compared with respective baseline values, pravastatin decreased LDL cholesterol and total cholesterol to a greater extent than hormone therapy (p = 0.0001 and 0.003 for difference between treatments, respectively). High-density lipoprotein (HDL) cholesterol levels decreased with hormone therapy, but did not change with pravastatin (p = 0.01). Lipoprotein(a) decreased significantly with hormone therapy only (-14%, 95% confidence interval (CI) -21 to -6%, p = 0.01 for difference between groups). Brachial artery flow-mediated dilatation (FMD) was impaired at baseline, and this increased with hormone therapy (absolute mean change in artery diameter as percentage units 2.07, 95% CI 0.57-3.57, p = 0.009) versus no change with pravastatin (0.19, 95% CI -1.1 to 1.5, p = 0.78), with a near-significant difference between the two groups (p = 0.058). A significant correlation between improved brachial artery FMD and reduction in LDL cholesterol was not observed. Fibrinogen decreased significantly in both treatment groups with no difference between treatments.

In postmenopausal hypercholesterolemic women, pravastatin and hormone therapy exhibited divergent effects. The former lowered total and LDL cholesterol more effectively, whereas hormone therapy lowered lipoprotein(a) significantly and improved brachial artery endothelium-dependent dilatation, independent of the reduction in LDL cholesterol. The modest increase in brachial artery FMD seen is consistent with hypercholesterolemia compromising endothelial integrity, and suggests that the important effect of estrogen on the endothelial microenvironment may be attenuated in women with endothelial dysfunction.