A comparison of the effects of two continuous HRT regimens on cardiovascular risk factors

In a study comparing the effects of two continuous HRT regimens on cardiovascular risk markers, 43 postmenopausal women were randomly assigned to receive either tibolone 2.5 mg/day (n=20) or 0.625 mg/day conjugated equine oestrogens plus continuous medroxyprogesterone acetate 5 mg/day (n=23). Serum lipoprotein levels, including LDL and HDL subfractions, oxidisability of LDL and serum nitrate/nitrite levels were determined before and during 12 weeks of therapy. Tibolone significantly reduced triglycerides (17.1%, P<0.01), HDL cholesterol (22.2%, P<0.001), and the ratio HDL(2)/HDL(3) cholesterol (20.2%, P<0.01). Total LDL cholesterol levels did not change significantly, although there was a downward trend in the LDLIII subfraction (12.0% reduction; P=0.06), percentage changes being positively correlated with percentage changes in triglyceride levels (r=0.60, P<0.01). Susceptibility of LDL to oxidation was significantly decreased (P<0.001), changes in lag-time being highly negatively correlated with percentage changes in levels of both LDLIII (r=-0.68, P<0.01) and triglycerides (r=-0.63, P<0.01). Nitrate/nitrite levels did not change. In contrast, the combined therapy caused a significant reduction in LDL cholesterol levels (11.1%; P<0.01) as a result of a significant decrease in the LDLI+II subfraction (12.8%; P<0.05). Changes in LDLI+II and LDLIII were correlated with changes in triglyceride levels (r=-0.52, P<0.05 and r=0.63, P<0.01, respectively). No other parameter was significantly modified. Between treatment effects were significantly different on triglycerides (P<0.01), HDL cholesterol (P<0.001), LDL oxidation (P<0.01) and LDLI+II:LDLIII ratio (P<0.05). The reduction in LDL induced by the continuous combined therapy is likely to be beneficial, despite the apparent shift towards the LDLIII subfraction. Changes in oxidisability and subfraction profile of LDL indicate that tibolone may have a more favourable effect on cardiovascular risk than previously suggested.