Estrogen replacement therapy in combination with continuous intrauterine progestin administration reduces the amount of circulating oxidized LDL in postmenopausal women: dependence on the dose of progestin

BACKGROUND. Oxidized low density lipoprotein (LDL) plays a key role in processes leading to atherosclerosis. Recent studies show that LDL oxidation in vitro is effectively prevented by estrogen. Yet, the effect of hormonal therapy (HT) on in vivo LDL oxidation has remained open. AIM. We used a novel methodology for the measurement of oxidized LDL in vivo in order to investigate the effects of HT. METHODS. The subjects were derived from two separate trials. In trial 1 (24 months) women (n = 32) used intrauterine system releasing 10 mug/day levonorgestrel, and 2 mg oral estradiol. Trial 2 (12 months) consisted of two groups of subjects. One group (n = 30) used an intrauterine system releasing 20 mug/day levonorgestrel, and 2 mg estradiol; the other group (n = 32) received orally a combination of I mg norethisterone acetate and 2 mg estradiol. Blood samples were taken at 6 months intervals. Estimation of in vivo LDL oxidation was based on determination of baseline diene conjugation in isolated LDL. RESULTS. Hormonal therapy in trial 1 decreased markedly in vivo LDL oxidation. The effect was seen after 6 months' HT and became more pronounced towards the end of study (41% decrease; P < 0.0001). Contrary to this, in trial 2 the two different kinds of hormonal therapy schemes did not affect in vivo LDL oxidation. CONCLUSIONS. The strong effect seen in trial 1 shows that intrauterine levonorgestrel with 2 mg estradiol can lower LDL oxidation in vivo. The results show that this effect depends on dosage of the progestin.