Small low-density lipoprotein particles in women with natural or surgically induced menopause

Objective: To investigate the mechanism of the decrease in the size of low- density lipoprotein (LDL) particles in women with natural menopause and wom en with surgically induced menopause. Methods: We measured plasma levels of total cholesterol; triglycerides; hig h-density lipoprotein (HDL) cholesterol; apolipoproteins A-I, A-II, and B; and sex hormones in 45 women; 15 women were premenopausal, 15 were naturall y postmenopausal, and 15 were surgically menopausal, Lipoprotein lipase and hepatic triglyceride lipase activities were measured in postheparin plasma . Concentrations of total cholesterol and of apolipoprotein B in LDL also w ere measured. Low-density lipoprotein particle diameter was determined by g radient gel electrophoresis. Results: Plasma levels of total cholesterol, triglycerides, apolipoprotein B, LDL-total cholesterol, LDL-apolipoprotein B, and the activity of posthep arin plasma lipoprotein lipase were significantly higher and concentrations of estrone and estradiol were significantly lower in the naturally postmen opausal and surgically menopausal women than in the premenopausal women. Pl asma levels of HDL cholesterol and apolipoproteins X-I and A-II and posthep arin plasma hepatic triglyceride activity did not differ significantly betw een groups. The diameter of LDL particles was significantly reduced in the naturally (25.29 +/- 0.19 nm) and surgically (25.29 +/- 0.22 nm) menopausal women compared with the premenopausal women (25.88 +/- 0.22 nm). plasma tr iglyceride levels were negatively correlated with LDL particle diameter in all three groups (premenopausal group: -0.62, P < .01; naturally postmenopa usal group: r = -0.62, P < .01; and surgically menopausal group: r = -0.76, P < .001). The prevalence of LDL subclass pattern B was significantly incr eased in the naturally (67%, P < .05) and surgically (60%, P < .05)menopaus al women. Conclusion: The plasma concentration of LDL particles was increased after m enopause, whether natural or surgically induced. An increase in plasma trig lyceride levels in women with low levers of endogenous estrogen appeared to cause the size of LDL particles to be reduced. (Obstet Gynecol 1999;93:566 -70. (C) 1999 by The American College of Obstetricians and Gynecologists.).