The effects of estrogen administration (ethinyl estradiol; 0.1 mg, orally, daily) on plasma lipoprotein metabolism were investigated in five normolipidemic premenopausal females. Estrogen administration resulted in significant (P less than 0.05) mean increases in plasma cholesterol, triglyceride, very low density lipoprotein (VLDL)-cholesterol, and high density lipoprotein (HDL)-cholesterol of 18.8%, 87.0%, 123.1%, and 38.3%, respectively. Analytical ultracentrifugation demonstrated that HDL increases occurred mainly in the HDL2b subfraction (150.0% increase). Lipoprotein compositional analysis showed that estrogen administration caused significant increases in all VLDL and HDL constituents (protein, cholesterol, phospholipid, and triglyceride) as well as VLDL apolipoprotein (apo) B (118.9% increase) and HDL apoA-I (27.4% increase). No significant changes in LDL constituents were noted. Measurement of lipoprotein lipase and hepatic lipase enzymic activity in post-heparin plasma revealed no major change in lipoprotein lipase activity, but showed a significant decrease (43.8%) in hepatic lipase activity during estrogen administration. Radioiodinated VLDL and HDL kinetic data indicated increased VLDL apoB (86.1% rise) and HDL apoA-I (24.9% rise) synthesis during estrogen administration. These data are consistent with the concept that estrogen administration at the dose level studied in premenopausal females causes significant elevations in VLDL and HDL constituents, associated with enhanced production of VLDL apoB and HDL apoA-I.

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A B S T R A C T The daily transport of human plasma apolipoproteing A-I and A-II, triglyceride, and total cholesterol from the thoracic duct lymph into plasma was measured in two subjects before and three subjects after renal transplantation. Lymph triglyceride transport was -83% of the daily ingested fat loads, whereas lymph cholesterol transport was consistently greater than the amount of daily ingested cholesterol. Lymph apolipoprotein transport significantly (P < 0.05) exceeded the predicted apolipoprotein synthesis rate by an average of 659±+578 mg/d for apolipoprotein A-I and 109+59 mg/d for apolipoprotein A-II among the five subjects. It is estimated that 22-77% (apolipoprotein A-I) and 28-82% (apolipoprotein A-II) ofdaily total body apolipoprotein synthesis takes place in the intestine.Lymph high density lipoprotein particles are mostly high density lipoprotein2b and high density lipoprotein2a and have a greater overall relative triglyceride content and a smaller relative cholesteryl ester content when compared with homologous plasma high density lipoproteins. The major quantity ofboth lymph apolipoprotein A-I (81±8%) and apolipoprotein A-II (90±11%) was found within high density lipoproteins with almost all of the remainder found in chylomicrons and very low density lipoproteins.