A lipoprotein-containing particle is transferred from the serum across themammary epithelium into the milk of lactating mice

To investigate the role of low-density lipoprotein (LDL) in the delivery of cholesterol to the mammary gland during pregnancy and lactation, ive exami ned the distribution of radioactivity from I-125-tyramine cellobiose-LDL in jected into the tail vein of female mice at various stages of the reproduct ive cycle, Changes in the proportion of isotope taken up by the mammary gla nd largely reflected the increased weight of the gland in pregnancy and lac tation. In addition, during lactation, radioactivity tvas found in the milk and was associated with a protein of the molecular weight of apoB-100, Qua ntitatively similar results were obtained with mice homozygous for disrupti on of the LDL receptor gene (LDLR null). Analysis of endogenous lipoprotein s showed that the milk lipoprotein particles were denser than the correspon ding serum lipoproteins and largely depleted of triglyceride and cholestero l, Using fluorescence microscopy we visualize the sorting of apoB protein f rom the LDL lipid phase at the basal surface of the mammary epithelial cell of both wild-type and LDLR-null mice.j/r Our findings provide evidence tha t the mammary epithelium of the lactating mouse is able to take up LDL from the plasma by a non-LDLR-mediated process. An apoB-containing particle fro m which the cholesterol has been removed is transferred into milk.-Monks,J. , P. U. Huey, L. Hanson, R. H. Eckel, M. C. Neville, and S. Gavigan. A lipo protein-containing particle is transferred from the serum across the mammar y epithelium into the milk of lactating mice,J.