AN EXAMINATION OF THE EFFECT OF COMBINED CYCLICAL HORMONE REPLACEMENTTHERAPY ON LIPOPROTEIN(A) AND OTHER LIPOPROTEINS

Lipoprotein(a) (Lp(a)) is an independent marker of cardiovascular dise ase which is relatively unresponsive to treatment with most of the com monly prescribed lipid lowering drugs. Concentrations of Lp(a) increas e after the menopause, and the primary aim of this study was to determ ine whether combined hormone replacement therapy was effective in lowe ring levels of Lp(a) in postmenopausal women. An open longitudinal stu dy was conducted among 42 women who had undergone a spontaneous menopa use and were attending the outpatient clinic of the Prince of Wales Ho spital, Hong Kong. All subjects were treated with 2 mg oral estradiol daily and 5 mg medroxyprogesterone acetate for 12 days each calendar m onth. Fasting blood samples for lipoprotein measurement were taken bef ore the commencement of treatment and at 6 and 12 months. Lp(a) levels showed a skewed distribution with a median value before treatment of 9.45 mg/dl (range 1.47-95.62 mg/dl). After 6 months, there was a reduc tion to 7.70 mg/dl (1.12-72.59 mg/dl) (P < 0.01), and after 12 months the median concentration was 7.14 mg/dl (0.63-69.23 mg/dl) (P < 0.001 0-12 months). There were also significant reductions in the concentrat ions of apo B from 116.13 to 111.62 mg/dl and LDL-C from 3.02 to 2.74 mmol/l (P < 0.05), plus a lowering of TC of borderline significance. A po A-I increased from 162.56 to 173.35 mg/dl (P < 0.01), but there wer e no significant changes in; HDL-C or the HDL-C subfractions. TC, LDL- C, apo B and TG concentrations were higher and HDL-C and HDL(2)-C conc entrations were lower when blood was sampled during combined treatment with estrogen and progesterone than when estrogen was being taken alo ne. Levels of Lp(a) were also lower during the estrogen only phase of treatment, but none of these differences were statistically significan t. This study demonstrates that combined cyclical hormone replacement therapy is effective in reducing concentrations of Lp(a). The trend to wards a more atherogenic lipid profile during the combined phase of,tr eatment suggests that attention should be given to the timing of blood sampling in future studies of this nature.