Aortic plaque size and endometrial response in cholesterol-fed rabbits treated with estrogen plus continuous or sequential progestin

MPA and postmenopausal coronary artery atherosclerosis revisited

Whether progestins, particularly medroxyprogesterone acetate (MPA), attenuate the cardiovascular benefits of postmenopausal estrogen replacement therapy (ERT) has been controversial for over a decade. Concerns related first to findings that MPA attenuated increases of high density lipoprotein cholesterol (HDLC) concentrations of postmenopausal women compared to conjugated equine estrogen (CEE) alone. That observation was followed by early cynomolgus monkey studies that suggested MPA decreased estrogen's cardiovascular benefits (vascular reactivity and coronary artery atherosclerosis inhibition). In a more recent and larger trial with cynomolgus monkeys, no differences were seen in the coronary artery atherosclerosis protective effect of CEE when MPA was co-administered (HRT). The lack of attenuation of ERTs benefits by progestins has also been seen in at least three studies of carotid artery intima-media thickness (IMT) of postmenopausal women. Additionally, the majority of studies of vascular reactivity of postmenopausal women have not found differences when CEE is given alone or with MPA. Seven observational studies of cardiovascular outcomes of postmenopausal women permit separate consideration of ERT versus HRT use; there is no evidence of attenuation of ERTs benefits by progestin use. In conclusion, it is evident that the current experimental, clinical, and observational data do not provide evidence that progestins attenuate estrogen's cardiovascular benefits.

Effects of estradiol, cyproterone acetate, tibolone and raloxifene on uterus and aorta atherosclerosis in oophorectomized cholesterol-fed rabbits

BACKGROUND

Different hormonal replacement regimens are used for treating climacteric complaints; however, not all of them have the same clinical profile. Cardiovascular disease (CVD) is a major health problem and tibolone, raloxifene, estradiol (alone or with cyproterone acetate) have been added to cholesterol-fed rabbits to study atherosclerosis.

METHODS

A total of 48 cholesterol-fed New Zealand white rabbits were studied for 4 months. Forty rabbits underwent bilateral ovariectomy and the other eight were sham operated (group S). The ovariectomized rabbits were allocated to five groups of eight animals each receiving tibolone (Group T, 6 mg/day), raloxifene (R, 35 mg/day), estradiol valerate (E, 3 mg/day), estradiol valerate plus cyproterone acetate (EC, 3+0.5 mg/day, respectively), and no treatment for the control group (C). The sham group received no treatment too.

RESULTS

After 4 months the percentage of the extent of atherosclerosis in the aorta was 30.4% in C group, 24.5% in S group, 10.2% in T group, 30.3% in R group, 17.9% in E group and 28.1% in EC group (P<0.05 T vs. C, R, EC). The aortic cholesterol content compared with aortic weight was 8.55 microg/mg in C group, 11.97 microg/mg in S group, 1.86 microg/mg in T group, 3.82 microg/mg in R group, 2.86 microg/mg in E group and 5.24 microg/mg in EC group (P<0.05 T vs. EC, C, S; R vs. C, S; E vs. C, S). Uterine weights in grams were: 1.89 (C group), 2.24 (S), 7.38 (T), 1.94 (R), 9.92 (E), and 5.94 (EC); P<0.05 (C, S, R, vs. T, E, EC; T vs. E; EC vs. T, E).

CONCLUSION

Our study showed a decrease in the extent of aortic atherosclerosis in oophorectomized cholesterol-fed rabbits treated with tibolone or estradiol, and a decrease in aortic cholesterol content in rabbits treated with tibolone, raloxifene and estradiol. However, rabbits treated with tibolone showed an increased uterine weight, which is contrary to that observed in humans.

The menopause and HRT. Hormone replacement therapy, cardiovascular and cerebrovascular disease

Historically, research into vascular effects of hormone replacement therapy (HRT) poignantly highlights the difficulties in extrapolating from medical research into clinical practice. Original observational trials encouraged great enthusiasm that HRT was protective against coronary heart disease (CHD) in post-menopausal women. This was supported by a plethora of beneficial mechanistic effects of HRT on the vascular system. In contrast, recent controlled trials have shown that a specific combined oral HRT actually causes a small increased risk of cardiovascular and cerebrovascular events, compared to placebo. The absolute risks were small, yet were accompanied by increased venous thrombosis and breast cancer. Although many controversies still remain regarding the vascular effects of specific types of HRT, currently, in my opinion, all HRT should be considered as causing a small increased risk of vascular events, until proven otherwise. However, the apparent lack of HRT effectiveness in the prevention of vascular disease should not deter enthusiasm for the use of established preventive therapies, especially lifestyle measures.

Intimal plaque development and oxidative stress in cholesterol-induced atherosclerosis in New Zealand rabbits

Although oxidative stress is well known in atherogenesis, the origin, nature and kinetics of free radicals involved have not been well described till now. Here, we correlated parameters of oxidative stress with cellular components during induction and stabilization of aortic intimal lesions which were induced in rabbits by feeding a cholesterol-enriched diet for 6 weeks and a normal diet for further 68 weeks. Plasma lipids, aortic plaque size and composition (macrophages, smooth muscle cells, oxidized LDL by morphometry), as well as aortic radical production (by luminol-enhanced chemiluminescence and TEMPO-9AC fluorescence) were measured after various time points. The parameters of oxidative stress were correlated with the different cellular components of the aortic plaques. The plaques increased until week 21, no significant regression was found until week 74, plasma cholesterol was maximal at week 6. Macrophages, oxidized LDL and generation of different species of free radicals were increased during plaque development, yet with different time kinetics. Whereas chemiluminescence correlated only weakly with the amount of intimal macrophages, strong correlations were found between TEMPO fluorescence and smooth muscle cells (r = 0.4778, P < 0.001) and between macrophages and oxidized LDL (r = 0.5896, P < 0.0001). Different indicators of oxidative stress were increased during plaque progression and stabilization. However, the various correlations show, that distinct types of reactive species secreted probably from macrophages and smooth muscle cells contribute to oxidative stress in the different phases of plaque development.

Cyproterone acetate could counteract the benefits of estradiol valerate in oophorectomized cholesterol-fed rabbits

OBJECTIVE

The administration of hormonal replacement treatment to women with an intact uterus needs to be supplemented with progestogenic compounds to avoid endometrial hyperplasia. However, progestins may cancel the beneficial effects of estrogens on the cardiovascular system. The goal of this study was to examine the effects of adding cyproterone acetate to estradiol (E(2))on aorta atherogenesis.

DESIGN

Thirty-two cholesterol-fed New Zealand white rabbits were studied for 4 months. The animals underwent laparotomy and were randomly allocated to four groups. Twenty-four rabbits underwent bilateral ovariectomy, and the other eight were sham-operated (group S). The ovariectomized rabbits were allocated to three groups of eight animals each receiving E(2) valerate (group E), E(2) valerate plus cyproterone acetate (group EC), or placebo after sterilization (group C).

RESULTS

After 4 months, the cholesterol-rich diet caused atherosclerotic aortic lesions in both treated groups that affected 17.91% +/- 10.19% and 28.16% +/- 7.97% of the aortic surface of groups E and EC, respectively, with a markedly lower aortic plaque size in group E than in groups C and S. Rabbits from group E (but not from group EC) had aortic cholesterol content significantly lower than rabbits from the sham-operated and control groups.

CONCLUSION

E(2) valerate reduces aortic atheromatosis in cholesterol-fed, ovariectomized rabbits, and the addition of cyproterone acetate may neutralize this effect.