ESTROGEN-INDUCED SMALL LOW-DENSITY-LIPOPROTEIN PARTICLES IN POSTMENOPAUSAL WOMEN

Objective: To investigate the mechanisms of an estrogen-induced decrea se in the size of low-density lipoprotein (LDL) particles in postmenop ausal women. Methods: Twenty postmenopausal women were treated with co njugated equine estrogen, 0.625 mg daily, for 3 months. Plasma levels of total cholesterol, triglyceride, high-density lipoprotein (HDL) cho lesterol, and apolipoproteins AI, AII, and B were measured before and after therapy. We analyzed total, free, and esterified cholesterol, tr iglyceride, phospholipid, and apolipoprotein B levels in the LDL. Chol esterol, triglyceride, and phospholipid concentrations were measured b y enzymatic methods. Apolipoprotein Al, All, and B levels were determi ned by immunoturbidimetric assay. The diameter of LDL particles was de termined by gradient gel electrophoresis. Results: Estrogen reduced si gnificantly the plasma levels of total cholesterol and apolipoprotein B and increased significantly the plasma levels of triglyceride, HDL c holesterol, and apolipoproteins AI and AII. The ratio of cholesteryl e ster to apolipoprotein B was significantly reduced, whereas the ratio of triglyceride to apolipoprotein B was significantly increased after such treatment. The plasma level of triglyceride showed a positive cor relation with the ratio of LDL-triglyceride/apolipoprotein B (r =.40, P <.01), and a negative correlation with the ratio of LDL-cholesteryl ester/apolipoprotein B (r = -.55, P <.001). Estrogen treatment reduced significantly the diameter of LDL particles [25.79 +/- 1.13 nm versus 24.94 +/- 1.02 nm, P <.001). The diameter of the LDL particle was cor related negatively with the plasma level of triglyceride (r = -.84, P <.001) and the ratio of LDL-triglyceride/apolipoprotein B (r = -.58, P < .001), and positively with the ratio of LDL-cholesteryl ester/apoli poprotein B (r =.57, P <.001). Conclusion: The results of this study i ndicate that an increase in the triglyceride plasma level induced by e strogen therapy appeared to produce small triglyceride-rich and choles teryl ester-poor LDL particles that were of small size. (C) 1998 by Th e American College of Obstetricians and Gynecologists.).