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Journal of Human Hypertension (2000) 14, 99–104 2000 Macmillan Publishers Ltd All rights reserved 0950-9240/00 $15.00 www.nature.com/jhh ORIGINAL ARTICLE A randomised placebo controlled trial of the effects of tibolone on blood pressure and lipids in hypertensive women G Lloyd1, E McGing1, A Cooper1, N Patel1, PJ Lumb2, AS Wierzbicki2 and G Jackson1 1 Department of Cardiology and 2Chemical Pathology, Guys and St Thomas’ Hospital Trust, Lambeth Palace Road, London SE1 7EH, UK The effects of hormone replacement therapy in hypertensive women are controversial. This randomised placebo controlled trial assessed the effect of tibolone 2.5 mg on blood pressure and fasting plasma lipids in 29 hypertensive postmenopausal women over 6 months using a 2:1 randomisation to tibolone. The primary clinical end-point was mean office blood pressure. At 6 months systolic blood pressure declined by 5.30 ⴞ 2.87% vs 4.94 ⴞ 3.37% whilst diastolic blood pressure declined 5.38 ⴞ 2.65% vs 0.85 ⴞ 3.69% on tibolone and placebo respectively. These differences were not statistically significant. Triglycerides decreased by 33.3 ⴞ 6.1% vs 7.6 ⴞ 7.9% (P ⬍ 0.01) and high-density lipoprotein (HDL)-cholesterol by 21.7 ⴞ 3.8% vs 2.4 ⴞ 2.6% (P ⬍ 0.01) with tibolone as opposed to placebo. No significant differences were observed in total cholesterol, low-density lipoprotein (LDL)-cholesterol and lipoprotein (a). Fibrinogen levels were reduced by 13.6 ⴞ 6.8% on tibolone compared to a 19.3 ⴞ 15.4% rise (P ⬍ 0.05) on placebo. This study suggests that tibolone has no deleterious effect on blood pressure in women with hypertension but has contrasting effects on biochemical risk factors. Largescale studies are required to determine the overall effect of tibolone on cardiovascular morbidity and mortality. Journal of Human Hypertension (2000) 14, 99–104 Keywords: hormone replacement; hypertension; lipids; trial Introduction The role of hormone replacement therapy (HRT) in women with hypertension remains controversial. Oestrogen-based HRT remains underused in these women probably because of concerns about blood pressure deterioration in younger women taking the oral contraceptive.1 However, the potentially beneficial effects of HRT in reducing coronary heart disease (CHD) risk would suggest a role for it in the management of hypertension.2,3 The loss of oestrogen at the menopause appears to be associated with an overall rise in blood pressure.4 Little information is available regarding the long-term effects of HRT in hypertensive women, but short duration studies in hypertensive women have demonstrated either a neutral or even modest hypotensive effect.5–10 Cyclical HRT preparations are unacceptable to most women suffering from coronary disease or hypertension. Tibolone is a novel steroid compound, which controls menopausal symptoms,11 inhibits postmenopausal bone loss12 and augments forearm blood flow.13 It does not induce endometrial hyperplasia or, usually, postmenopausal bleeding.14 We investigated the effect of introducing tibolone in Correspondence: Dr Guy Lloyd, Cardiothoracic Department, 6th Floor, East Wing, St Thomas’ Hospital, London SE1 7EH, UK Received 24 May 1999; revised and accepted 3 September 1999 women with pre-existing hypertension on both blood pressure and biochemical cardiovascular risk factors. Materials and methods Study design The trial had a double-blind, randomised, placebocontrolled format. Randomisation was 2:1 in favour of tibolone to increase the probability of demonstrating a treatment effect. The study received local ethical approval and written informed consent was obtained. At two baseline visits clinical details, baseline blood pressure, quality of life parameters and fasting lipid profiles were measured. Patients were reviewed monthly for continued blood pressure assessment. Baseline biochemical investigations were repeated at the final clinical visit after 6 months treatment. Eligibility Eligible patients had previously diagnosed hypertension on or off treatment with antihypertensives. All had three separate standard mercury sphygmomanometer blood pressure readings greater than 160/90 mm Hg over 3 months or were taking longterm antihypertensive treatment. All were 1 or more years postmenopausal on clinical grounds. Exclusion criteria included, intrinsic renal disease, Tibolone randomised controlled trial G Lloyd et al 100 insulin-dependent diabetes or a past history of an oestrogen dependent tumour. Women who had used sex steroid compounds including oral contraception, previous HRT, progesterone, tibolone or tamoxifen within the previous 3 months were excluded. Blood pressure measurement Blood pressure was measured as near as possible at the same time of the same day of the week by one of two operators using the British Hypertension Society approved methods.15 For the purposes of analysis the mean of the three recumbant blood pressure measurements was calculated. If blood pressure exceeded 210/120 mm Hg on two separate visits, the patient left the study to allow modification of medication, otherwise all concomitant antihypertensive medication was left unchanged for the duration of the study. Plasma lipids and lipoproteins Blood samples were drawn in the recumbant position after a 12-h fast. Samples were centrifuged immediately and stored at −70°C until subsequent analysis. Plasma lipid profiles were detained in a single batch by standard automated methods for total cholesterol, triglycerides and HDL on a Cobas Fara II analyser. Low-density lipoprotein (LDL) was calculated by the Freidewald equation if triglycerides ⬍4.5 mmol/L. Apolipoprotein (apo) A1, A2, B, lipoprotein (a) [Lp(a)] and fibrinogen were measured by immunoturbidimetric methods on the same analyser. Lp(a) samples were pre-treated by centrifugation and lipase treatment to reduce any triglyceride interference with the assay. All methods used were validated against International Federation of Clinical Chemistry standards and had standard deviations of ⬍2.5% for lipids, ⬍4% for apolipoproteins, ⬍6% for Lp(a) and ⬍3% for fibrinogen for medium range calibrators. Quality of life Quality of life was recorded at baseline and at 6 months using the SF-36 General Health Questionnaire.16 This measures eight health concepts: physical functioning, physical and emotional role limitations, bodily pain, general health, vitality, social functioning, mental health and reported health transition. In each measure, a higher score indicates a better health state. Statistical analysis The study was powered to detect a change in mean blood of 15 mm Hg. A 2:1 randomisation was used to increase the power to detect a treatment effect while accepting an increased risk of a type I error. In patients who dropped out of the study the blood pressure at the last visit was carried forward to successive visits. Blood pressure data were analysed on an intention-to-treat basis but percentage change in lipid values was calculated only for those patients who finished the study and were taking medication Journal of Human Hypertension at the final visit. Data were analysed using the SPSS statistical package (version 6.0). Parametric data are displayed as mean and standard error, non-parametric data as median and range while frequency data as value and percentage. Principal analysis was performed using ANOVA for repeated measures with unpaired t-testing for individual two-way comparisons between subjects allocated to tibolone or placebo. Non-parametric data (lipoprotein (a) and triglycerides) were compared using the appropriate non-parametric test (Mann–Whitney) with contingency table testing of frequency data (Yates’ continuity correction). P ⬍ 0.05 was considered statistically significant. Results Demographics Major demographic features were similar in the active and placebo arms of the study (Table 1). The mean age of the women was 60.1 years in the active group and 62.7 years in the placebo group. Both groups were more than 10 years after the menopause (11.5 years tibolone and 16.1 years placebo). There were non-significant statistical differences in other patient characteristics and in concomitant medications. Blood pressure Study blood pressure readings are recorded in Figure 1 and Table 2. The entry mean blood pressure was 161 ± 5.2/91 ± 1.8 mm Hg in the tibolone group and 157 ± 5.4/85 ± 2.4 mm Hg in the placebo. Baseline diastolic blood pressure was slightly but significantly higher in the active treatment arm (P ⬍ 0.05) but the mean arterial pressure was not significantly different (126.0 ± 3.2 vs 121.2 ± 3.6 mm Hg). Systolic blood pressure fell by 5.2%, diastolic pressure by 3.6% and mean arterial pressure by 4.6%. After 6 months the blood pressures were 151 ± 5.5/87 ± 3.4 mm Hg in the active and 148 ± 4.1/84 ± 3.2 mm Hg in the placebo arm. Neither absolute or percentage reductions in systolic and diastolic blood pressures were significantly different at 6 months. Similarly the pulse pressure was unaffected by allocation to treatment arm. Lipids, lipoproteins and fibrinogen Biochemical data from the trial are presented in Table 2 and Figure 2. Total cholesterol fell in both arms of the study with no difference between tibolone and placebo groups. The reduction in total cholesterol in the placebo group was however statistically significant (P = 0.04). LDL-cholesterol rose slightly by 1.2 ± 8.0% in the tibolone group compared with a 5.3 ± 2.5% fall on placebo. High-density lipoprotein (HDL) was significantly reduced (21.7 ± 3.8%) falling from 1.40 ± 0.1 to 1.08 ± 0.1 mmol/L with tibolone compared to a 2.4 ± 2.6% rise in those on placebo. Similarly apolipoprotein A-1 fell by 20.4 ± 3.6% compared with a 2.5 ± 2.1% rise on placebo but ApoAII levels Tibolone randomised controlled trial G Lloyd et al 101 Table 1 Patient characteristics Age Current smoker Never smoked Non-caucasian Duration of hypertension (years) Last menstrual period (years) Weight (kg) Height BMI Drug therapy ACE inhibitor AT II antagonists Beta-blockers Calcium antagonists Diuretics Vastatin No previous antihypertensives Previous HRT Tibolone (n = 19) Placebo (n = 11) 60.11 2 7 1 10.5 11.5 77.77 160.32 33.90 (1.28) (11%) (39%) (6%) (2.20) (1.84) (5.38) (4.10) (5.99) 62.73 1 8 1 11.45 16.10 77.11 161.48 29.60 (1.79) (9%) (73%) (9%) (2.86) (3.78) (3.09) (2.23) (1.30) 0.35 1.0 0.17 1.00 0.68 0.30 0.40 0.59 0.79 3 1 8 5 5 2 6 3 (16%) (5%) (44%) (28%) (28%) (11%) (33%) (17%) 2 1 9 3 5 1 0 3 (18%) (10%) (82%) (27%) (46%) (9%) 1.00 1.00 0.11 1.00 0.57 1.00 0.09 0.83 (27%) Significance (P =) No values significantly different at the 0.05 level. declined less than ApoAI with tibolone therapy. Triglycerides were reduced by 33.4 ± 6.1% on tibolone compared to 7.6 ± 7.9% on placebo (P ⬍ 0.05). Fibrinogen was reduced on tibolone by 13.5 ± 6.8% but rose by 19.3 ± 15.4% on placebo (P ⬍ 0.05). Median Lp(a) rose nonsignificantly in both groups during the study but final levels were similar. Quality of life There were no significant differences within the tibolone and placebo groups between baseline and 6-month follow-up: Figure 1 Effects of tibolone and placebo on systolic and diastolic blood pressure. general health: 68.2 (5.0) vs 65.4 (4.9) tibolone, 66.1 (7.4) vs 71.7 (5.2) placebo; physical functioning: 64.2 (9.1) vs 64 (6.9) tibolone, 66.1 (10.8) vs 71.9 (6.2) placebo; physical role: 58.3 (16.7) vs 58.3 (13.2) tibolone, 62.5 (18.3) vs 78.1 (14.5) placebo; emotional role: 81.5 (11.3) vs 96.9 (3.0) tibolone. 62.5 (18.3) vs 70.83 (15.9) placebo; social functioning: 90 (5.2) vs 80.1 (7.7) tibolone, 70.3 (9.7) vs 80.4 (10.2) placebo; bodily pain: 70.3 (8.2) vs 65.3 (8.3) tibolone, 68.7 (11.13) vs 71.5 (11.4) placebo; vitality: 52.8 (8.8) vs 51.9 (6.2) tibolone, 52.5 (8.8) vs 52.1 (8.9) placebo; mental health: 78.7 (3.9) vs 81.0 (3.4) tibolone, 66.5 (9.3) vs 65.6 (9.1) placebo. There were also no significant differences between the tibolone and placebo group at baseline or 6-month follow-up. Adverse events Figure 2 Effects of tibolone and placebo on the percentage change on cardiovascular risk factors. (쏔) Placebo, (쐽) Tibolone. *P ⬍ 0.05. Both tibolone and placebo were well tolerated. Four patients taking tibolone (22%) developed some vaginal bleeding compared with one (9%) in the placebo arm; this difference was not statistically significant. One patient in the placebo group developed a major vaginal bleed resulting in hospitalisation Journal of Human Hypertension Journal of Human Hypertension (5.28) (0.27) (1.45–2.60) (0.09) (0.33) (0.30) (0.07) (0.01) (0.08) (0.11) (5–66) (0.43) (13.2–30.1) 72.20 6.23 2.11 1.24 3.88 3.21 1.54 0.56 1.47 1.50 14 3.49 19.6% 69.86 6.12 1.54 1.40 3.82 2.86 1.67 0.51 1.39 1.30 10 3.37 11.1% (4.45) (0.38) (1.22–2.44) (0.06) (0.36) (0.31) (0.05) (0.03) (0.11) (1.40) (7.5–23) (0.20) (8.6–19.1) 85.11 (2.38)* 157.30 (5.83) Placebo 91.11 (1.76) 160.97 (5.18) *P ⬍ 0.05; Tribolone vs placebo. a Framingham model for systolic blood pressure. Systolic blood pressure (mm Hg) Diastolic blood pressure (mm Hg) Pulse pressure (mm Hg) Total cholesterol (mmol L) Triglycerides (mmol L) HDL-C (mmol L) LDL-C (mmol L) LDL: HDL ratio Apo AI (mmol L) Apo AII (mmol L) Apo B (mmol L) Apo B: (A1–A2) ratio Lipoprotein (a) Fibrinogen 10-year cardiac riska Tibolone Baseline Table 2 Change in blood pressure, lipids, apolipoproteins and fibrinogen 64.16 5.73 1.23 1.08 4.03 4.02 1.32* 0.51 1.44 1.88* 9 3.01* 13.2% (3.08) (0.39) (0.83–1.54) (0.06) (0.41) (0.57) (0.05) (0.02) (0.11) (0.20) (6–33) (0.19) (10.4 –22.8) 86.63 (3.38) 151.39 (5.07) Tibolone Placebo 63.97 5.63 1.31 1.28 3.49 2.76 1.56 0.51 1.31 1.28 15 3.44 13.5% (4.87) (0.38) (1.03–2.12) (0.09) (0.39) (0.31) (0.09) (0.03) (0.09) (0.13) (4 –16) (0.15) (8.5–19.8) 84.09 (3.11) 148.06 (4.05) Month 6 (7.14) (5.66) (6.06) (3.78) (8.00) (9.30) (3.57) (3.28) (8.28) (14.69) (20.74) (6.81) (57.2–20.4) −10.05 −6.75 −7.61 −2.42 −5.29 −2.75 −2.47 −2.04 −7.37 −4.38 −7.87 19.32 −15% (4.50) (2.58) (7.93) (2.63) (2.45) (2.45) (2.13) (2.61) (3.74) (5.15) (26.81) (15.37) (7.0–32.1) −0.85 (3.69) −5.38 (2.65) −1.55 −9.78 −33.37* −21.66* 1.21 30.41* −20.37* −8.31 3.42 46.10* −10.93 −13.55* 18.6% −4.94 (3.37) Placebo −5.30 (2.87) Tibolone Percent change from baseline Tibolone randomised controlled trial G Lloyd et al 102 Tibolone randomised controlled trial G Lloyd et al and subsequent dilatation and curettage. Two patients (11%) in the tibolone arm and two (18%) in the placebo arm terminated the study early: two (one active and placebo) because of side effects (headache, nausea and flushing), one because of the development of an intercurrent pneumonia deemed not to be related to study medication, and one for personal reasons. Discussion The menopause may play a role in the acceleration of hypertension in women. A rise in diastolic blood pressure and a steepening of the time dependent rise in systolic blood pressure occur in the postmenopause.4 Concurrently other adverse changes occur in cardiac risk factors including rises in LDL and insulin resistance, falls in HDL, and changes in fat distribution.17 Gender protection is lost so the incidence of CHD in women equals that in men by the age of 65.18 Hypertensive women in the Nurses Health Study had a 3.5-fold increase in risk of CHD with a 2.6-fold increase in stroke compared with nonhypertensives.19 Despite circumstantial evidence of benefit, HRT has only rarely been prescribed in hypertensive women, possibly due to the known hypertensive effects of oestrogen seen in women on the contraceptive pill.1 However oestrogen and progestin supplementation may be beneficial in postmenopausal women with hypertension. Oestrogen acts as a vasodilator by restoring impaired endothelial function,20 inhibiting the vasoconstrictor actions of endothelin-l21 and by inhibiting the influx of Ca2+ ions into vascular smooth muscle cells.22 In addition oestrogen reduces circulating catecholamines levels23 and may act as an angiotensin-converting enzyme inhibitor.24 In vivo administration of oestrogen or natural progesterone can bring about an acute drop in blood pressure.5,6 In hypertensive women a number of small studies have documented an antihypertensive effect. Transdermal oestradiol can reduce daytime systolic pressure,7 achieve an absolute reduction in overall pressures8 and restore a normal 24-h ambulatory blood pressure profile.9 Other studies have shown no effect of oestrogens on blood pressure in the hypertensive population but a reduction in plasma renin and aldosterone levels.10 The use of HRT alongside antihypertensive therapy can offset some of the adverse metabolic effects associated with drugs such as thiazides and beta-blockers.25 Not all studies have shown encouraging results. A study of a retirement community in the USA found a relationship between the incidence of hypertension and both dose and duration of oestrogen use.26 Another small sequential series noted a rise in blood pressure associated with oestrogen use that returned to normal following termination of oestrogen therapy.27 The PEPI study in normotensive women showed that oestrogen plus various progestins did not alter blood pressure significantly over a 3-year period.2 Tibolone is a synthetic steroid with the unusual property of differential metabolism in different organs. Hence it exerts a progesterone-like inhibitory effect on breast28 and uterine tissue29 and relieves menopausal symptoms11 while preventing bone loss12 much like oestrogen. Tibolone augments forearm11 and aortic blood flow,30 and alters aortic distensibility,31 which suggest it may reduce blood pressure. It has also been reported to reduce myocardial ischaemia in women with angina.32 Furthermore in an atherosclerotic rabbit model tibolone significantly reduced the development of new atherosclerotic plaque.33 It has androgenic effects on plasma lipids especially in reducing HDL. This study shows tibolone has no differential effect on HDL-cholesterol uptake and transfer as HDL and apoA1 levels were reduced in parallel. The effects of tibolone on HDL affect apoA1 more than apoA2, implying deleterious effects on reverse cholesterol transport is HDL:A1 but not HDL:A1:A2 dependent. It also may have differential effects on apoA gene expression as these genes are usually co-ordinately regulated. Alterations in lipid risk factors for CHD such as triglycerides and Lp(a) may outweigh the effects of tibolone on HDL.34 –36 It is of note that cholesterol levels fell significantly in the placebo group. This is difficult to understand as no specific dietary advice was given and lipidlowering therapy was held as a constant throughout the study. Presumably partaking in a clinical study caused subjects to have heightened awareness of cardiac risk factors and pay more attention to diet and lifestyle issues. This randomised placebo-controlled trial demonstrated no clinically significant alteration in blood pressure in hypertensive women taking tibolone for 6 months. The study, though small, was powered to detect a clinically relevant change in blood pressure that might affect clinical decision-making (15 mm Hg). These results support the findings of a large observational study of tibolone which found no rise in blood pressure in 75 hypertensive menopausal women over 14 months.37 The effects of tibolone on lipids were similar to those previously described with a 20–25% fall in HDL. The adverse effect on the LDL:HDL, apoB: apoA1 and apoB:(apoA1-A2) ratios imply that tibolone interfered with reverse cholesterol transport and for this reason may be deleterious. However, the 33% reduction in triglycerides and 19% reduction in fibrinogen may counterbalance this effect. In the most current model of cardiac risk derived from the Framingham study, incorporating TC, HDL-C and other risk factors, tibolone increased cardiac risk by about 18% but this was not statistically significant and in this population represented a rise in absolute risk of 2.6%.38 A fall in Lp(a) with tibolone has been noted but this was not reproduced here.35 The measurement of Lp(a) is difficult to standardise and subject to wide variation so both studies are likely to be underpowered. Larger scale studies of the effects of tibolone on Lp(a) are required. Tibolone was well tolerated and did not significantly effect the quality of life. 103 Conclusions Tibolone at a dose of 2.5 mg is safe to use in women with treated or untreated hypertension, with miniJournal of Human Hypertension Tibolone randomised controlled trial G Lloyd et al 104 mal effects on blood pressure. The balance between its adverse effects on HDL and the beneficial effects on triglycerides and fibrinogen should be the subject of further study in women at risk of CHD. 19 20 Acknowledgements The authors would like to thank Organon Laboratories LTD for the supply of the study medications and for an educational grant towards this study, and The Peel Medical Research Trust. 21 22 References 1 Khaw KT, Peart WS. Blood pressure and contraceptive use. Br Med J 1982; 285: 403– 407. 2 The writing group for the PEPI trial. Effects of oestrogen or oestrogen/progestin regimens on heart disease risk factors in postmenopausal women. JAMA 1995; 273: 199–208. 3 Grodstein F et al. Post menopausal oestrogen and progestin use and the risk of cardiovascular disease. New Engl J Med 1996; 335: 435– 461. 4 Staessen J et al. The influence of menopause on blood pressure. J Hum Hypertens 1989; 3: 427– 433. 5 Luotola H. Blood pressure and haemodynamics in postmenopausal women during 17-beta oestradiol substitution. Annals Clinical Res 1983; 15 (Suppl 38): 8–85. 6 Rylance P et al. Natural progesterone and antihypertensive action. Br Med J 1985; 290: 13–14. 7 Manhem K, Ahlm H, Milsom I, Svenssson A. Transdermal oestrogen reduces daytime blood pressure in hypertensive women. J Hum Hypertens 1998; 12: 323–327. 8 Mercuro G et al. Effects of acute administration of transdermal oestrogen on postmenopausal women with systemic hypertension. Am J Cardiol 1997; 80: 652–655. 9 Zoncu S et al. Estradiol 17 beta reduces blood pressure and restores the normal amplitude of circadian pressure rhythm in postmenopausal hypertensive women. Eur Heart J 1997; 18: 3119 (abstract). 10 Kornhauser C, Malacara J, Garay M, Perez-Luque E. The effect of hormone replacement therapy on blood pressure and cardiovascular risk factors in women with moderate hypertension. J Hum Hypertens 1997; 7: 405– 411. 11 Ross LA, Alder EM. Tibolone and climacteric symptoms. Maturitas 1995; 21: 127–136. 12 Lindsay R, McKhart D, Krauss RM. prospective double blind trial of synthetic steroid (Org OD 14) for preventing postmenopausal osteoporosis. Br Med J 1980; 280: 1207–1209. 13 Hardiman P, Nihoyannopoulos P, Kicovic P, Ginsburg J. Cardiovascular effects of Org OD 14 a new steroidal therapy for climacteric symptoms. Maturitas 1991; 13: 235–242. 14 Ginsberg J, Prelevic G, Butler D, Okolo S. Clinical experience with tibolone (Livial) over 8 years. Maturitas 1995; 21: 71–76. 15 Petrie JC, O’Brien ET, Littler WA, de Swiet M. Recommendations on BP measurements. Br Med J 1986; 293: 611–615. 16 Ware JE, Sherbourne CD. The MOS-36 item short form health survey (SF-36), conceptual framework and item section. Medical Care 1992; 30: 473– 478. 17 Mathews K et al. Menopause and risk factors for coronary heart disease. New Engl J Med 1989; 321: 641–646. 18 Kannel W, Hjortland M, McNamara P, Gordon T. MenoJournal of Human Hypertension 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 pause and the risk of cardiovascular disease. The Framingham study. Ann Intern Med 1976; 85: 447–552. Fiebach N et al. A prospective study of high blood pressure and cardiovascular disease in women. Am J Epidemiol 1989; 130: 646–653. Gilligan DM, Quyyumi AA, Cannon RO. Effects of physiological levels of estrogen on coronary vasomotor function in postmenopausal women. Circulation 1994; 89: 2545–2551. Zhang F, Ram JL, Standley PR, Sowers JR. 17- oestodiol attenuates voltage-dependent Ca2+ currents in A7r5 vascular smooth muscle cell line. Am J Physiol 1994; 266: C975–C980. Jiang C, Sarrel P, Poole-Wilson P, Collins P. Acute effects of 17-beta estradiol on rabbit coronary artery contractile responses to endothelin 1. Am J Physiol 1992; 263 (1 pt 2): H271–H275. Rosano G et al. Effects of estrogen replacement on heart rate variability and heart rate in healthy postmenopausal women. Am J Cardiol 1997; 80: 815–817. Proudler A et al. Hormone replacement therapy and serum angiotensin converting enzyme activity in postmenopausal women. Lancet 1996; 346: 89–90. Christiansen C et al. Effects of natural estrogen/Gestagen and thiazide on coronary risk factors in normal postmenopausal women. Acta Obstet Gynecol Scand 1981; 60: 407– 412. Pfeffer R. Estrogen use, hypertension and stroke in postmenopausal women. J Chronic Dis 1978; 31: 389–398. Crane M, Harris J, Windsor W. Hypertension, oral contraceptive agents and conjugated estrogens. Ann Intern Med 1971; 74: 13–21. Colacurci N et al. Effects of tibolone on the breast. Eur J Obstet Gynaecol Reprod Biol 1998; 80: 235–238. Okon M, Lee S, Laird S, Li T. A prospective randomised controlled study comparing the morphological and biochemical responses of the endometrium to two different forms of ‘period-free’ hormone replacement therapy. Hum Reprod 1998; 13: 2261–2265. Prevelic G, Beljic T, Ginsburg J. The effect of tibolone on cardiac flow in postmenopausal women with noninsulin dependent diabetes mellitus. Maturitas 1997; 27: 85–90. Lehmann ED et al. Aortic distensibility in post-menopausal women receiving tibolone. Br J Radiol 1994: 67: 701–705. Lloyd G et al. Acute effects of hormone replacement with tibolone on myocardial ischaemia in women with angina. Int J Clin Pract 1998; 52: 155–157. Zandberg P et al. Tibolone prevents atherosclerotic lesion formation in cholesterol-fed ovariectomised rabbits. Arteriosclerosis Thromb Vase Biol 1998; 18: 1844 –1854. Walker I et al. The effect of the synthetic steroid ORG OD 14 on fibrinolysis and blood lipids in postmenopausal women. Thromb Haemostasis 1985; 53: 303–305. Rymer J et al. Effects of tibolone on serum concentrations of lipoprotein (a) in postmenopausal women. Acta Endocrinologica 1993; 128: 259–262. Hanggi W et al. Long term influence of different postmenopausal hormone replacement regimens on serum lipids and Lipoprotein (a): a randomised study. Br J Obstet Gynaecol 1997; 104: 708–717. Lip G, Beevers M, Churchill D, Beevers DG. Hormone replacement therapy and blood pressure in hypertensive women. J Hum Hypertens 1994; 8: 491– 494. Wood D et al. Joint British recommendations in the prevention of coronary heart disease in clinical practice. Heart 1999; 80 (Suppl 2): S12–S19.