Effects in post-menopausal women of transdermal estrogen associated with progestin upon the removal from the plasma of a microemulsion that resembles low-density lipoprotein (LDL)

Objective: To evaluate the effects of transdermal estradiol and medroxyprogesterone acetate (MPA) treatment on the removal from the plasma of a cholesterol-rich microemulsion (LDE) that roughly resembles low-density lipoprotein (LDL) structure and that binds to LDL receptors. Methods: Ten healthy post-menopausal women were studied before and after 3-month treatment with transdermal estradiol in the following dosages administered every 3.5 days: 25, 50, 50, 100, 100, 50, 50 and 25 μg. From the 15th to the 21st day and from the 22nd to the 28th day of estrogen treatment, respectively, 10 and 5 mg q.d. MPA per oral were associated to the transdermal estrogen. The emulsion labeled with ¹⁴C-cholesteryl oleate was injected after 12 h fasting and its fractional catabolic rate (FCR) was calculated from the plasma decaying curves of the isotope. Results: Treatment reduced LDL-cholesterol levels by 8% only (149.0 ± 36.0 mg/dl, 138.0 ± 27.0 mg/dl; P = 0.046), but the FCR of LDE expressed in medians (25%; 75%) increased from 0.0054 (0.003; 0.052) h⁻¹ to 0.021 (0.009; 0.10) h⁻¹, P = 0.002. Conclusion: The association used in this study so as to mimic the increasing–decreasing pattern of the hormonal ovarian production reduced modestly LDL-cholesterol levels but pronouncedly increased the lipoprotein removal as tested by LDE FCR.