Hormonal regulation of lipoprotein(a) levels: effects of estrogen replacement therapy on lipoprotein(a) and acute phase reactants in postmenopausal women.

Estrogen lowers lipoprotein(a) [Lp(a)] levels, but the mechanisms involved have not been clarified. To address the relationship between estrogenic effects on Lp(a) and serum lipids, and on other plasma proteins of hepatic origin, 15 healthy postmenopausal women participated in a randomized, double-blinded, placebo-controlled, crossover study with 4 weeks of oral conjugated estrogens (0.625 mg/d) and placebo, separated by a 6-week period. Lp(a) levels decreased during estrogen treatment in 14 of the 15 subjects (mean decrease, 23%; P < .001). In response to estrogen, apolipoprotein A-I (apoA-I), HDL cholesterol, and triglyceride levels increased by 12% (P = .001), 11% (P < .001), and 10% (P = .02), respectively. Apolipoprotein B (apoB) and LDL cholesterol levels decreased by 7% (P = .01) and 12% (P = .03), respectively, ApoB, LDL cholesterol, and Lp(a) levels fell within 1 week of treatment, whereas apoA-I and HDL cholesterol levels rose more slowly. Levels of acid alpha 1-glycoprotein (AAG) and haptoglobin (HPT), two hepatically derived acute phase proteins, also decreased during estrogen treatment by 18% (P < .001) and 25% (P = .002), respectively. Although the changes in AAG and HPT in response to estrogen were highly correlated (r = .67, P = .009), we were unable to detect a correlation between change in either acute phase protein and change in Lp(a) (r = -.14 and -.24, P = .64 and .41). The lack of correlation between the changes in two acute phase reactants and Lp(a) suggests different underlying mechanisms for the effects of estrogen on these liver-derived proteins.

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