The effect of
17 alpha-dihydroequilin sulfate (DHES), a water-soluble
estrogen of
conjugated estrogens (
Premarin), and ethynylestradiol (EE), a commonly used
estrogen found in many
oral contraceptives, on the development of
atherosclerosis was studied in rabbits fed an atherogenic diet (0.2%
cholesterol) for 24 weeks. Ten animals were given 15 micrograms. kg-1.d-1 EE, 10 received 3.8 mg.kg-1.d-1 of DHES, and the remaining 10
sham-ovariectomized and 10 ovariectomized animals served as
cholesterol-fed controls. These doses were chosen to have similar estrogenic potency. Plasma
cholesterol concentrations increased to about 900 mg/dL and did not differ among the experimental groups. After 24 weeks, plasma
beta-VLDL and
HDL cholesterol concentrations were the same for all
cholesterol-fed groups, while
LDL cholesterol was significantly higher in the two
estrogen-treated groups. In spite of this, both EE and DHES significantly reduced
atherosclerosis by 35% in the aortic arch and 75% to 80% in the thoracic and abdominal aorta. The reduction in
atherosclerosis was seen in animals with a wide range (400 to 1400 mg/dL) of plasma
cholesterol concentrations and was independent of
lipoprotein profile.
beta-VLDL isolated from
estrogen-treated animals was not significantly different from control
beta-VLDL in its ability to stimulate
cholesterol accumulation in THP-1 macrophages in culture. This suggests that the protective effect of
estrogens on the development of
atherosclerosis is not mediated by qualitative differences in
beta-VLDL that affect uptake by macrophages. The results of this study extend our knowledge of the range of
estrogens that reduce
atherosclerosis. Given the lack of effect on plasma
lipid and
lipoprotein concentrations, these data are consistent with the conclusion that
estrogens exert some of this beneficial effect directly at the level of the arterial wall by influencing certain key components in the pathogenesis of
atherosclerosis.