The impact of female sex hormones on secondary prevention of atherosclerosis in ovariectomized cholesterol-fed rabbits

The present study investigated the effect of female sex hormones and diet on atherosclerotic arteries in rabbits. The animals were initially ovariectomized and then fed an atherogenic diet for 12 weeks (n = 60). They were thereafter randomized to 5 groups of which one immediately was killed. Three of the remaining groups received a moderate atherogenic diet plus oral 17β-estradiol, levonorgestrel or no hormones, whereas the last group was fed a diet without hormones or cholesterol. During the second phase of the study, the rabbits receiving the moderate atherogenic diet and no hormones had the highest serum concentration of cholesterol (48.0 ± 3.4 mmol/l), whereas those having the cholesterol free diet had the lowest value (26.4 ± 3.6 mmol/l) with the two hormone groups in between (mean ± S.E.M., P < 0.05). The estradiol group had only approximately half of the aortic accumulation of cholesterol (854 ± 155, nmol/mg) found in the levonorgestrel (1676 ± 362) and moderate atherogenic diet (1829 ± 361) groups (mean ± S.E.M., P < 0.05). The estradiol group and the rabbits fed diet without hormones or cholesterol (1034 ± 169) had a comparable degree of atherosclerosis. In conclusion, estradiol inhibits progression of atherosclerosis significantly. This beneficial effect is only partly explained by changes in serum lipids and lipoproteins.