Contrasting effects of two hormone replacement therapies on the cardiovascular and mammary gland outcomes in surgically postmenopausal monkeys

Timing of hormone therapy, type of menopause, and coronary disease in women: data from the National Heart, Lung, and Blood Institute-sponsored Women's Ischemia Syndrome Evaluation

OBJECTIVE

The aim of this study was to assess the relationship of the timing of hormone therapy (HT) use with angiographic coronary artery disease (CAD) and cardiovascular disease (CVD) events in women with natural versus surgical menopause.

METHODS

We studied 654 postmenopausal women undergoing coronary angiography for the evaluation of suspected ischemia. Timing and type of menopause, HT use, and quantitative angiographic evaluations were obtained at baseline, and the women were followed for a median of 6 years for CVD events.

RESULTS

Ever users of HT had a significantly lower prevalence of obstructive CAD compared with never users (age-adjusted odds ratio, 0.41 [0.28-0.60]). Women with natural menopause initiating HT before age 55 years had lower CAD severity compared with never users (age-adjusted β [SE] = -6.23 [1.50], P < 0.0001), whereas those initiating HT at age 55 years or more did not differ statistically from never users (-3.34 [2.13], P = 0.12). HT use remained a significant predictor of obstructive CAD when adjusted for a "healthy user" model (odds ratio, 0.44 [0.30-0.73]; P = 0.002). An association between HT and fewer CVD events was observed only in the natural menopause group (hazard ratio [95% CI], 0.60 [0.41-0.88]; P = 0.009) but became nonsignificant when adjusted for the presence or severity of obstructive CAD.

CONCLUSIONS

Using the quantitative measurements of the timing and type of menopause and HT use, earlier initiation of HT was associated with less angiographic CAD in women with natural but not surgical menopause. Our data suggest that the effect of HT use on reduced cardiovascular event rates is mediated by the presence or absence of angiographic obstructive atherosclerosis.

The Mammary Glands of Macaques

This review describes the normal biology and physiology of the mammary gland in macaques, including the typical histologic appearance across the life span (development, reproductive maturity, lactation, and senescence). The molecular events regulating breast morphogenesis are described, as well as systemic and local hormonal regulators of mammary gland proliferation, differentiation, and function. Similarities and differences to the human breast are described. Regulatory events are illuminated by discussion of genetically modified mouse models. Tissue response markers, including immunohistochemical markers of proliferation and other hormonally induced changes and studies to date, regarding the effects of exogenous hormones, are briefly summarized. In general, estrogens stimulate progesterone receptor expression and proliferation in the mammary gland, and combinations of estrogens and progestogens cause greater proliferation than estrogens alone. Evaluation of novel chemical agents in macaques requires careful evaluation of age and hormonal context to avoid the confounding effects of mammary gland development, past reproductive history, and other influences on mammary gland morphology. The expression of proliferation markers and progesterone receptors may be used as biomarkers to measure chemically induced hormonal effects.

Effects of hormone therapy and dietary soy on myocardial ischemia/reperfusion injury in ovariectomized atherosclerotic monkeys

OBJECTIVE

Hormone therapy (HT) and dietary soy (Soy) inhibit myocardial ischemia/reperfusion (I/R) injury in nonatherosclerotic animals. The aim of this study was to determine their independent and interactive effects on I/R in monkeys previously fed an atherogenic diet for 15 months.

DESIGN

Ovariectomized atherosclerotic monkeys (n = 40) were divided into one of four dietary treatment groups: (1) casein as the protein source, (2) casein and added HT (the equivalent of 5 mug ethinyl estradiol + 1 mg norethindrone acetate daily), (3) Soy protein providing 141 mg total isoflavones daily, or (4) Soy + HT. After 12 months monkeys were anesthetized, and their left anterior descending coronary artery was occluded for 1 hour and reperfused for 4 hours. Infarct size was the percentage of the area at risk not staining with triphenyltetrazolium chloride. Additional measures were myocardial blood flow, stroke volume, coronary output, myeloperoxidase, and malondialdehyde.

RESULTS

There was an interactive negative effect of HT + Soy to increase infarct size from approximately 30% (in other groups) to 55% (P = 0.0004). Additionally, there were negative main effects of Soy on blood flow, coronary output, and stroke volume during I/R (all P values <0.05). There were no effects of treatment on either myeloperoxidase or malondialdehyde.

CONCLUSIONS

Neither HT nor Soy had beneficial effects, whereas their combination had harmful effects, on myocardial I/R injury in monkeys with preexisting atherosclerosis. The mechanism of this negative interaction remains unclear but may relate to Soy's negative effects on hemodynamics.

The long-term impact of 2-3 years of hormone replacement therapy on cardiovascular mortality and atherosclerosis in healthy women

OBJECTIVE

The effect of hormone replacement therapy (HRT) on cardiovascular risk is intensely debated. The aim of this study was to investigate the long-term effects of HRT given for a few years on all-cause and cardiovascular mortality and the severity of atherosclerosis.

METHODS

This analysis was based on a cohort of 1,458 postmenopausal women (55.8 +/- 6.1 years old) who previously participated in a number of randomized, placebo-controlled, clinical trials assessing the efficacy of 2-3 years of therapy with various estrogen plus progestin combinations for preventing bone loss. Women were followed on average for 9.8 years and came for a follow-up visit. Outcome variables were all-cause and cardiovascular mortality and the severity of atherosclerosis, as estimated by semi-quantitative scoring of vascular calcification in the lumbar aorta on lateral radiographs.

RESULTS

A total of 174 women died during the observation period. All-cause mortality was decreased by 30% in the HRT+ group compared with the HRT- group (hazard ratio (HR) 0.70; 95% confidence interval (CI) 0.50-0.97) after adjusting for age, body mass index and smoking. Under the same conditions, similar results characterized mortality from cardiovascular disease (n = 61 deaths; 35.1% of all deaths) and coronary heart disease (n = 39 deaths; 22.4% of all deaths), which were decreased by 46% (HR 0.54, 95% CI 0.29-0.98, p = 0.045) and 53% (HR 0.47, 95% CI 0.21-1.03, p = 0.062), respectively. Furthermore, the mean severity score of aortic calcification at follow-up was significantly lower in hormone-treated compared to non-treated women (p < 0.0001).

CONCLUSION

Women who receive 2-3 years of HRT after menopause do not have increased all-cause mortality, and results of the present study suggest relative cardiovascular benefits compared to those who had not used hormones.

Hormone therapy and cardiovascular risk markers and disease: focus on progestagens

Biological studies have demonstrated estrogen's beneficial effect on cardiovascular risk factors, including plasma lipoproteins, atherogenesis, vascular reactivity, inflammation and antioxidative activity. Additionally, observational studies have supported a cardioprotective effect of hormone therapy (HT), although an underlying healthy-user effect may account for these observations. Progestagens are added to protect against an increased risk of endometrial cancer observed with unopposed estrogen treatment. The inclusion of progestagen in HT has been associated with possible adverse cardiovascular outcomes. Recent, large-scale, randomized clinical studies did not confirm a beneficial cardiovascular effect of HT. On the contrary, an increased risk was found with continuous combined estrogen-progestagen regimens. The progestagen used in these trials was medroxyprogesterone acetate and other progestagen components have only been sparsely elucidated. The purpose of the present review is to outline some of the modifying effects of different progestagens on the actions of estrogen on cardiovascular risk markers and clinical end points observed in biological, observational and clinical studies.

The effect of medroxyprogesterone acetate on estrogen-dependent risks and benefits--an attempt to interpret the Women's Health Initiative results

The results of the two arms of the Women's Health Initiative (WHI) study allow a comparative assessment of the contribution of the progestogen component to the changes in risk of cardiovascular disease and cancer during treatment of postmenopausal women with conjugated equine estrogens and medroxyprogesterone acetate (CEE/MPA). However, the high proportion of older and overweight or obese women compromises any conclusions, since we estimate that 50% of the women would have the metabolic syndrome. In overweight postmenopausal women with hyperinsulinemia, the risk of breast cancer is elevated and cannot be increased further by hormone replacement therapy (HRT). Therefore, the non-significant, but consistent reduction in breast cancer risk during treatment with CEE alone might be based on an improvement of hyperinsulinemia. The 24% increase in breast cancer risk in the CEE/MPA group can be regarded as an artifact due to very low numbers of breast cancer diagnoses in the placebo group of women who had received HRT prior to the WHI study. The elevated risk of venous thromboembolism and the transient increase in the risk of coronary heart disease (CHD) during treatment with CEE/MPA but not CEE alone suggests a direct effect of MPA on the vessel wall. MPA has been demonstrated to upregulate the thrombin receptor, the thrombin-induced production of tissue factor and procoagulatory activity in the vessel wall owing to its glucocorticoid activity. In contrast, CEE alone reduced non-significantly the risk of CHD in women aged 50-59 years, suggesting that primary prevention is possible if estrogen replacement therapy is initiated early. As clinical studies on the effect of different progestogens combined with estrogens are scarce, a possible superiority of progestogens other than MPA remains to be proven.

2-methoxyestradiol inhibits differentiation and is cytotoxic to osteoclasts

2-Methoxyestradiol (2-ME), a naturally occurring metabolite of 17beta-estradiol, is highly cytotoxic to a wide range of tumor cells but is harmless to most normal cells. However, 2-ME prevented bone loss in ovariectomized rats, suggesting it inhibits bone resorption. These studies were performed to determine the direct effects of 2-ME on cultured osteoclasts. 2-ME (2 microM) reduced osteoclast number by more than 95% and induced apoptosis in three cultured osteoclast model systems (RAW 264.7 cells cultured with RANKL, marrow cells co-cultured with stromal support cells, and spleen cells cultured without support cells in media supplemented with RANKL and macrophage colony stimulating factor (M-CSF)). The 2-ME-mediated effect was ligand specific; 2-hydroxyestradiol (2-OHE), the immediate precursor to 2-ME, exhibited less cytotoxicity; and 2-methoxyestrone (2-MEOE1) the estrone analog of 2-ME, was not cytotoxic. Co-treatment with ICI 182,780 did not antagonize 2-ME, suggesting that the cytotoxicity was not estrogen receptor-dependent. 2-ME-induced cell death in RAW 264.7 cells coincided with an increase in gene expression of cytokines implicated in inhibition of differentiation and induction of apoptosis. In addition, the 2-ME-mediated decrease in cell survival was partially inhibited by anti-lymphotoxin(LT)beta antibodies, suggesting that 2-ME-dependent effects involve LTbeta. These results suggest that 2-ME could be useful for treating skeletal diseases in which bone resorption is increased, such as postmenopausal osteoporosis and cancer metastasis to bone.

Pharmacology of estrogens and progestogens: influence of different routes of administration

This review comprises the pharmacokinetics and pharmacodynamics of natural and synthetic estrogens and progestogens used in contraception and therapy, with special consideration of hormone replacement therapy. The paper describes the mechanisms of action, the relation between structure and hormonal activity, differences in hormonal pattern and potency, peculiarities in the properties of certain steroids, tissue-specific effects, and the metabolism of the available estrogens and progestogens. The influence of the route of administration on pharmacokinetics, hormonal activity and metabolism is presented, and the effects of oral and transdermal treatment with estrogens on tissues, clinical and serum parameters are compared. The effects of oral, transdermal (patch and gel), intranasal, sublingual, buccal, vaginal, subcutaneous and intramuscular administration of estrogens, as well as of oral, vaginal, transdermal, intranasal, buccal, intramuscular and intrauterine application of progestogens are discussed. The various types of progestogens, their receptor interaction, hormonal pattern and the hormonal activity of certain metabolites are described in detail. The structural formulae, serum concentrations, binding affinities to steroid receptors and serum binding globulins, and the relative potencies of the available estrogens and progestins are presented. Differences in the tissue-specific effects of the various compounds and regimens and their potential implications with the risks and benefits of hormone replacement therapy are discussed.

New progestagens for contraceptive use

The progestins have different pharmacologic properties depending upon the parent molecule, usually testosterone or progesterone (P), from which they are derived. Very small structural changes in the parent molecule may induce considerable differences in the activity of the derivative. In hormonal contraceptives, progestins represent the major agent designed for suppressing ovulation and are used in combination with estrogen (E) usually ethinyl-estradiol (EE). The development of new generations of progestins with improved selectivity profiles has been a great challenge. Steroidal and nonsteroidal progesterone receptor (PR) agonists have been synthesized as well, although the latter are still in a very early stage of development. Several new progestins, have been synthesized in the last two decades. These include dienogest (DNG), drospirenone (DRSP), Nestorone (NES), nomegestrol acetate (NOMAc) and trimegestone (TMG). These new progestins have been designed to have no androgenic or estrogenic actions and to be closer in activity to the physiological hormone P. DRSP differs from the classic progestins as it is derived from spirolactone. It is essentially an antimineralocorticoid steroid with no androgenic effect but a partial antiandrogenic effect. The antiovulatory potency of the different progestins varies. TMG and NES are the most potent progestins synthesized to date, followed by two of the older progestins, keto-desogestrel (keto-DSG) and levonorgestrel (LNG). The new molecules TMG, DRSP and DNG also have antiandrogenic activity. Striking differences exist regarding the side effects among the progestins and the combination with EE leads to other reactions related to the E itself and whether the associated progestin counterbalances, more or less, the estrogenic action. The 19-norprogesterone molecules and the new molecules DRSP and DNG are not androgenic and, therefore, have no negative effect on the lipid profile. Given their pharmacological properties, it is likely that the new progestins may have neutral effects on metabolic or vascular risks. However, this hypothesis must be confirmed in large clinical trials.

A comparison of two progestins on myocardial ischemia???reperfusion injury in ovariectomized monkeys receiving estrogen therapy

OBJECTIVE

It has been reported that the progestin medroxyprogesterone acetate (MPA), but not norethindrone acetate (NETA), inhibits the beneficial vascular effects of post-menopausal estrogen therapy, but their effects on the myocardium are unclear. The goal of this study is to compare the effects of these two progestins on post-ischemic myocardial damage.

METHODS

Ovariectomized monkeys were fed an atherogenic diet for 18 months while receiving, or not receiving (control, n=15), the monkey equivalent to a woman's dose of 5 mug ethinyl estradiol with either 1 mg NETA daily (n=15) or 2.5 mg MPA daily (n=15). The left anterior descending coronary artery was occluded for 1 h and then released to allow myocardial reperfusion for 4 h. Infarct size was quantified using the histochemical stain triphenyl-tetrazolium chloride. Regional myocardial blood flow was measured by 15 mum neutron-activated microspheres, blood pressure and heart rates with a pneumatic cuff, stroke volume by echocardiography, coronary output by thermodilution and neutrophil accumulation in the myocardium using myeloperoxidase (MPO) activity.

RESULTS

The infarct size (area of necrosis/area at risk) was similar between the control group (21+/-3%) and the MPA group (29+/-3%) (P<0.05) but significantly less in the NETA group (3+/-2%) than other groups (P<0.05). The hemodynamic myocardial function and regional myocardial blood values were similar among groups before, during and 4 h after reperfusion (all P-values >0.05). Similarly, there were no treatment effects on MPO activity (P>0.05).

CONCLUSIONS

NETA, but not MPA, diminished ischemia-reperfusion injury in estrogen-treated post-menopausal females. The mechanism(s) of this difference remains unclear.

The effects of hormone replacement on the biomechanical properties of the uterosacral and round ligaments in the monkey model

OBJECTIVE

The purpose of this study was to determine effects of ovariectomy (OVX) and conjugated equine estrogens plus medroxyprogesterone acetate (CEE/MPA), or ethinyl estradiol plus norethindrone acetate (EE/NA) on biomechanics of uterosacral (USL) and round (RL) ligaments in postmenopausal (PMP) monkeys.

STUDY DESIGN

This was a randomized, triple blind, placebo-controlled study. OVX monkeys received 12 months no treatment (Pbo) (n = 19), CEE/MPA (n = 19), or EE/NA (n = 21). USL and RL step strains and stress-relaxation data were curve-fitted, giving strain-dependent tensile modulus (TM) from 0% to 30%.

RESULTS

(1) USL: TM for both treatment groups was greater than Pbo for strains from 0% to 12% (P < .04). (2) RL: TM for both treatment groups was smaller than Pbo for strains from 12% to 30% (P < .05). No differences were found between treatment regimens.

CONCLUSION

CEE/MPA and EE/NA both affect functional biomechanical properties by increasing tensile stiffness in the USL and decreasing it in the RL.

Breast cancer risk in the WHI study: The problem of obesity

In the climacteric, about 40% of the women have occult breast tumors the growth of which may be stimulated by hormones. Many genetic, reproductive and lifestyle factors may influence the incidence of breast cancer. Epidemiological data suggest that the increase in the relative risk (RR) of breast cancer induced by hormone replacement therapy (HRT) is comparable with that associated with early menarche, late menopause, late first birth, alcohol consumption, etc. One of the most important risk factors is obesity which exceeds the effect of HRT by far, and in overweight postmenopausal women the elevated risk of breast cancer is not further increased by HRT. As in the WHI study the majority of women was overweight or obese, this trial was unsuitable for the investigation of breast cancer risk. In the women treated with an estrogen/progestin combination, the RR of breast cancer rose only in those women who have been treated with hormones prior to the study, suggesting a selection bias. In the women not pretreated with hormones, it was not elevated. In the estrogen-only arm of the WHI study, there was no increase but a steady decrease in the RR of breast cancer during 6.8 years of estrogen therapy. This result was unexpected, as estrogens are known to facilitate the development and growth of breast tumors, and the effect is enhanced by the addition of progestins. Obese women are at high risk to develop a metabolic syndrome including insulin resistance and hyperinsulinemia. In postmenopausal women, elevated insulin levels are not only associated with an increased risk for cardiovascular disease, but also for breast cancer. This might explain the effects observed in both arms of the WHI study: HRT with relative low doses of estrogens may improve insulin resistance and, hence, reduce the elevated breast cancer risk in obese patients, whereas this beneficial estrogen effect may be antagonized by progestins. The principal options for the reduction of breast cancer risk in postmenopausal women are the prevention of overweight and obesity to avoid the development of hyperinsulinemia, the medical treatment of insulin resistance, the use of low doses of estrogens and the reduction of exposure to progestins. The latter might include long-cycles with the sequential use of appropriate progestins every 3 months for 14 days. There are large inter-individual variations in the proliferative response to estrogens of the endometrium. Control by vaginalsonography and progestin challenge tests may help to identify those women who may be candidates for low-dose estrogen-only therapy.

Appropriate use of hormones should alleviate concerns of cardiovascular and breast cancer risk

Since the publication of several recent randomized trials in the United States, prescriptions for hormonal therapy have dropped precipitously. This has been due, in large part, to the concerns about the increased risk of cardiovascular (CV) disease and breast cancer among the hormone users. This review takes the perspective that the appropriate use of hormones largely alleviates these concerns. The appropriate use of hormones pertains to treating younger, healthy women who have menopausal symptoms as well as using low-doses of hormones. In the randomized trials, suggesting an increased CV risk, the older women were largely asymptomatic and had other CV risk factors. Data are presented to suggest that there is no increased CV risk with hormonal therapy in younger, healthy women within 5 years of menopause. Moreover, a model is presented to attempt to explain the potential of preventing CV disease when estrogen is begun early, and the relative hazard associated with later use. The risk of breast cancer with hormonal therapy is put into perspective with the realization that this risk is related to hormonal dose and duration of use, and that the absolute risk remains small. Use of progestogens, in particular, appears to enhance this risk. The appropriate use of hormones also pertains to using lower-doses. Here data are presented showing efficacy with lower-doses and improved safety. With the use of lower-doses of estrogens, the progestogen dose, as required in women with a uterus, can be minimized.

Role of progestins with partial antiandrogenic effects

An experts' meeting on the 'Role of progestins with partial antiandrogenic effects' was held in Berlin from January 19 to 22, 2001. The meeting was chaired by Dr R. Sitruk-Ware (New York, USA) and participants included Ms F. Fruzzetti (Pisa, Italy), J. Hanker (Trier, Germany), J. Huber (Vienna, Austria), F. Husmann (Bad Sassendorf, Germany), S. O. Skouby (Copenhagen, Denmark), J. H. H. Thijssen (Utrecht, The Netherlands), and R. Druckmann (Nice, France). The present paper reports the conclusions of the meeting. However, the publication of the Women's Health Initiative study, which appeared after the meeting, led to additional comments and revisions.

Lessons to be learned from animal studies on hormones and the breast

The relation of hormone use by postmenopausal women to breast cancer risk has been controversial and unclear. A recent large randomized trial, the Women's Health Initiative (WHI) and a large observational study (Million Women Study) provided somewhat conflicting answers. The WHI found an increased incidence of breast cancer among women given hormone therapy (conjugated equine estrogen plus medroxyprogesterone acetate) but no increase in those given estrogen only therapy (conjugated equine estrogen alone). Whereas, the Million Women Study found an increased breast cancer risk among the estrogen plus progestin and the estrogen only users. This review brings comparative perspective to the issue of the effects of estrogen plus progestin versus estrogen only effects on breast cancer and is focused particularly on nonhuman primates. Although data from rodents is mixed, studies of monkeys suggest that estrogen only treatment has little or no effect on breast cell proliferation, and by inference, on breast cancer risk. On the other hand, data from both mouse and monkey studies strongly support the conclusion that the co-administration of a progestogen with an estrogen markedly increases breast cell proliferation and the potential for breast cancer promotion.

Exogenous progestagens and the human breast

The role of progestins (or progestagens) on the breast tissue remains controversial. However, according to the molecule and the duration of application, cell differentiation and apoptosis may predominate over proliferation. Progestins are also used as second-line agents for the treatment of metastatic breast cancer. In young women with benign breast disease, long-term treatment with 19-nortestosterone progestins had a trend to decrease breast cancer risk contrarily to what was observed in postmenopausal women receiving estrogens. Several compounds with progestational activity have been used for HRT. Small differences in the structure of the molecules may lead to pronounced differences in activities, some progestins exerting androgenic effects and some exerting estrogenic or glucocorticoid like activities. While most progestins do not bind to the estrogen receptors, it has been shown that some androgenic progestins stimulate MCF7 cells proliferation while progestins derived from progesterone did not induce cell multiplication in the same cell lines. Therefore, different progestins may induce different effects on the breast cells. Whether the progestins available to date are able to bind specifically to the progesterone receptors PR-A or PR-B and whether this is of clinical relevance to breast cell proliferation is still unclear. Although the relationship between progestin use and breast cancer risk is still the subject of debate and controversy, the data reported to date suggest that 5 years of treatment carry a low risk but further duration of use increases the risk. Further studies are still needed, randomised long-term prospective studies as well as from the laboratory, especially to determine whether a sequential or continuous regimen would be preferable as far as breast-cell response and apoptosis are concerned, and what are the effects of the various molecules used for HRT.

Medroxyprogesterone acetate antagonizes the effects of estrogen treatment on social and sexual behavior in female macaques

Medroxyprogesterone acetate (MPA) commonly is used in contraception and hormone replacement therapy. However, little is known about its effects within the central nervous system. Using ovariectomized pigtail macaques (Macaca nemestrina), we evaluated the potential for MPA to antagonize estradiol (E2) effects on female sociosexual behavior. Subjects (n = 6) were treated sequentially with placebo, E2 alone, E2 + progesterone (P4), and E2 + MPA. The order of treatments was balanced among subjects, and equimolar quantities of P4 and MPA were administered. During each treatment period, female sexual initiation rates, anxiety-related behavior, and aggression were recorded. Treatment with E2 alone induced a substantial rise in female sexual initiation rates. Although concurrent P4 treatment failed to significantly inhibit sexual behavior, MPA treatment markedly antagonized E2's effects. Neither the E2-only nor the E2 + P4 treatment had an impact on aggression rates, but the E2 + MPA treatment induced a significant rise in this behavior. Both MPA and P4 counteracted the effect of E2 on measures of anxiety. These findings suggest that MPA antagonizes certain behavioral effects of E2 that may be beneficial to women, and that it does so more profoundly or in ways that endogenous P4 does not. The marked increase in aggression seen during MPA treatment suggests that production of negative affect may be a particularly serious side effect of MPA.

Cervical and vaginal epithelial neoplasms in cynomolgus monkeys

Papillomavirus-associated cervical cancer is the second most common neoplasm in women but has rarely been reported in animals. This report describes cervical and vaginal intraepithelial neoplasms identified in routine histologic specimens obtained from 20 (5.2%) of 385 female cynomolgus macaques (Macaca fascicularis) being used in long-term studies. Lesion incidence was similar in both control and hormonally treated animals (4.7% and 5.5%, respectively). Neoplasms included benign vaginal papillomas, mild to severe intraepithelial dysplasias, and two invasive cervical carcinomas. Common morphologic features included koilocytosis, nuclear atypia, and expansion of the basal epithelium. Selective staining of lesions with at least one of three papillomavirus antibodies was observed in all cases (20 of 20). In contrast, immunostaining of lesions was negative for Epstein-Barr-related virus proteins (0 of 20). The unique similarities between the observed lesions and those seen in women suggest that macaques may provide a suitable animal model for study of papillomavirus oncogenesis.

New Progestogens

The progestins have different pharmacological properties depending upon the parent molecule, usually testosterone or progesterone, from which they are derived. Very small structural changes in the parent molecule may induce considerable differences in the activity of the derivative. In postmenopausal women with an intact uterus, progestins are used in combination with estrogen as hormone-replacement therapy (HRT). The development of new generations of progestins with improved selectivity profiles has been a great challenge. Steroidal and nonsteroidal progesterone-receptor (PR) agonists have been synthesised as well, although the latter are still in a very early stage of development. Several new progestins, which have been synthesised in the last 2 decades, may be considered fourth-generation progestins. These include dienogest, drospirenone, Nestorone (Population Council, New York, NY, USA), nomegestrol acetate and trimegestone. The fourth-generation progestins have been designed to have no androgenic or estrogenic actions and to be closer in activity to the physiological hormone progesterone. Drospirenone differs from the classic progestins as it is derived from spirolactone. It is essentially an antimineralocorticoid steroid with no androgenic effect but a partial antiandrogenic effect. The antiovulatory potency of the different progestins varies. Trimegestone and Nestorone are the most potent progestins synthesised to date, followed by two of the older progestins, 3-keto-desogestrel and levonorgestrel. The new molecules trimegestone, drospirenone and dienogest also have antiandrogenic activity. Following the publication of the results of the Women's Health Initiative study, the role of progestins in HRT became controversial. Unfortunately, this concern has been directed towards progestins as a class, although striking differences exist among the progestins. Natural progesterone and some of its derivatives, such as the 19-norprogesterone molecules, and the new molecules drospirenone and dienogest are not androgenic and, therefore, have no negative effect on the lipid profile. The effects of progestins on breast tissue remain controversial as well. However, depending on the progestin and the duration of application, breast cell differentiation and apoptosis may predominate over proliferation. It is still unclear if the currently available progestins are able to bind specifically to the PR isoforms PR-A or PR-B and whether this is of clinical relevance to breast cell proliferation is also unclear. Although it is likely that the new progestins may have neutral effects on the risk of coronary heart disease or breast cancer in younger postmenopausal women, this hypothesis must be confirmed in large randomised, well controlled clinical trials.

Hormone Replacement Therapy and Cardiovascular Disease: Lessons from a Monkey Model of Postmenopausal Women

Concerns exist about the cardiovascular effects of hormone replacement therapy (HRT) in postmenopausal women because results from the Women's Health Initiative (WHI) and the Heart and Estrogen/Progestin Replacement Study (HERS) are contradictory. In both of these studies, postmenopausal conjugated equine estrogens + medroxyprogesterone acetate did not reduce risk, and somewhat increased the risk of myocardial infarction in both primary (WHI) and secondary (HERS) prevention. These results appear to contradict numerous observational clinical trials and animal studies, which reported profound beneficial effects of HRT on cardiovascular disease risk. Results of both human and monkey studies indicate that estrogen replacement therapy (ERT)/HRT is effective in inhibiting progression of early stage (fatty streak) atherosclerosis but that ERT/HRT is much less effective in inhibiting progression of more advanced (established plaque) atherosclerosis. Results of these monkey studies are consistent with those of studies in women wherein ERT/HRT was initiated in postmenopausal women with different initial amounts of atherosclerosis. Based on these findings, it is speculated that ERT/HRT may be more cardioprotective in younger postmenopausal women with less coronary artery disease, and less effective in women with established coronary artery disease. Researchers are challenged to define the relative cardiovascular risk/benefit in different populations of postmenopausal women based on differences in age, amounts of pre-existing atherosclerosis, and risk factors.

Long-Cycle Treatment with Oral Contraceptives

The conventional regimen of oral contraceptive (OC) use mimics the natural cycles by causing regular withdrawal bleeding, which can be avoided by omission of the hormone-free interval of 7 days. Consequently, long-cycle regimens with continuous administration of OCs for 3 or 6 months followed by a hormone-free interval of 7 days may reduce the frequency of menstruations and cycle-dependent complaints. Surveys have revealed that, despite a higher rate of irregular bleeding, the majority of women prefer the long-cycle regimen to the conventional OC regimen with regular bleeds every 4 weeks because it may improve quality of life. As this regimen increases the contraceptive efficacy to a large degree, continuous treatment with OCs may prevent unintended pregnancies in women who miss a pill or are concomitantly treated with drugs that are able to impair the efficacy of OCs. Postponement of withdrawal bleeding may also reduce or prevent menses-associated disorders such as hypermenorrhoea and dysmenorrhoea, and have beneficial effects in patients with haemorrhagic diathesis, endometriosis, uterine leiomyoma and polycystic ovary syndrome. Continuous use of OCs prevents the cyclic fluctuations of serum levels of ethinylestradiol and progestogen and, hence, the cyclic variations of metabolic serum parameters. Although the long-cycle regimen is initially associated with an elevated rate of irregular bleeding, the total number of bleeding days that require sanitary product protection is lower than during conventional OC treatment. Many physicians tend to prescribe extended OC cycles for postponement of menstruation or reduction of frequency of regular bleeding. This review summarises and examines the available data on OC long-cycle regimens. The data suggest that the rate of treatment-related side effects with OCs according to the long-cycle regimen is similar to that of conventional OC regimens. However, clinical trials are necessary to assess the impact of long-term OC long cycles on safety, particularly the risk of cancer and cardiovascular disease, and fertility after discontinuation of treatment.

Hyper-reactivity of cerebral arteries from ovariectomized rats: therapeutic benefit of tamoxifen

1. An increased incidence of systemic hypertension has been documented in postmenopausal women and identified as an independent risk factor in the development of cerebrovascular stroke. The present study examined whether cerebrovascular reactivity was increased in the hypertensive ovariectomized rat, and explored the potential therapeutic benefit of the partial estrogen receptor agonist tamoxifen. 2. Female Sprague-Dawley rats were subjected to bilateral ovariectomy (OVX, n=16) or a sham operation (n=8). At 6-week postsurgery, rats were anesthetized to assess ventricular contractility and blood pressure. In a second series of experiments, OVX rats (n=8) were given tamoxifen starting 3 weeks postsurgery, and continued for 3 weeks. At the end of each protocol, the middle cerebral artery was harvested and rings were mounted in wire-myographs to measure isometric tension. 3. Systolic arterial pressure (SAP) was significantly increased (P<0.05) in the OVX rat (174+/-8 mmHg), as compared to sham (135+/-6 mmHg). The resting tension of isolated cerebral arteries from OVX rats (186+/-15 mg) was significantly elevated (P<0.05), as compared to sham (129+/-9 mg). Phenylephrine treatment did not elicit a constriction of cerebral arteries isolated from sham rats, whereas a potent response (P<0.05) was observed in OVX rats. Nitric oxide (NO) synthase inhibition with L-NNA led to a limited contraction in sham rats (8+/-3% of Emax), whereas a significant (P<0.05) increase was observed in OVX rats (34+/-12% of Emax). Lastly, vascular sensitivity (pD2) to sodium nitroprusside was significantly increased (P<0.05) in OVX rats, as compared to sham. 4. Tamoxifen therapy normalized the resting tension of isolated cerebral arteries from OVX rats, abrogated phenylephrine-mediated contraction, and modestly reduced SAP. By contrast, tamoxifen treatment of OVX rats did not attenuate L-NNA-mediated contractile response of cerebral arteries. 5. These data demonstrate that the cerebral artery isolated from the OVX rat was associated with an exaggerated vasoconstrictor response to phenylephrine, and altered NO-dependent vascular reactivity. The administration of tamoxifen to OVX rats normalized cerebral artery reactivity to phenylephrine. These findings provide the impetus to examine the potential therapeutic benefit of the partial estrogen receptor agonist tamoxifen to reduce the incidence of cerebrovascular stroke in postmenopausal women.