OBJECTIVE: Antioxidant and protective effect of high density lipoprotein (HDL) cholesterol for atherosclerosis is well known. The decrease of HDL concentration in postmenopausal women can be a reason for increased coronary artery disease due to atherosclerosis. The paraoxonase (PON) enzyme in blood is related with the antioxidant effect of HDL. Catalase (CAT), besides superoxide dismutase and glutathione peroxidase, is a natural antioxidant enzyme. Erythrocyte lipid peroxidation can be determined by the measurement of MDA, which is an index of oxidative damage. The objective of this study was to determine whether postmenopausal oestrogen replacement therapy has some effects on lipid peroxidation and antioxidative enzymes. Desing: Thirty women, who had undergone menopause after surgery for a benign disease, were included in this prospective study. Mean age of the patients was 49.30+-4.16 years. Every patient was given conjuge equine estrogen 0.625mg p.o. daily for 6 months. PON, CAT and MDA were measured before the therapy (baseline), at the first month and sixth month of the therapy. We used paired-t-test to evaluate our findings. Setting: University hospital Patients: Thirty women who had undergone menopause after surgery for a benign disease INTERVENTION: Women were administered conjugated equine estrogen 0.625mg p.o. daily for 6 months Main Outcome Measure: PON, CAT and MDA were measured before the therapy (baseline), at the first month and sixth month of the therapy RESULTS: The level of PON at baseline (PON1) was 65.79+-34.76 U/l, at the first month (PON2) was 34.76+-27.76 U/l and at the sixth month (PON3) was 76.93+-27.12 U/l. The p values for PON1-PON2, PON1-PON3 and PON2-PON3 were 0.308, 0.779 and 0.572; respectively. The level of erythrocyte CAT at baseline (CAT1) was 4600.88+-1056.04 U/g Hb, at the first month (CAT2) was 4675.74+-1487.01 U/g Hb and at the sixth month (CAT3) was 4393.31+-750.97 U/g Hb. The p values for CAT1-CAT2, CAT1- CAT3 and CAT2-CAT3 were 0.526, 0.448 and 0.689; respectively. The level of erythrocyte MDA at baseline (MDA1) was 27.85+- 7.96 nmol/mg protein, at the first month (MDA2) was 30.33+-9.66 nmol/mg protein and at the sixth month (MDA3) was 24.92+- 6.16 nmol/mg protein. The p values for MDA1-MDA2, MDA1-MDA3 and MDA2-MDA3 were 0.375, 0.147 and 0.179; respectively. There was no significant difference between any of the pairs above. CONCLUSION: Our study demonstrated no increase of PON and erythrocyte CAT activities and no change in erythrocyte MDA level due to oestrogen replacement therapy in postmenopausal women. On the other hand, some other studies showed beneficial effects of oestrogen replacement in preventing atherosclerosis. More detailed studies are necessary to investigate this subject.

Keywords: catalase, estrogen replacement therapy, paraoxonase