LIPOPROTEIN THYROID-HORMONE INTERACTIONS

A small but significant portion of the thyroid hormones that circulate in human plasma is associated with lipoproteins. Although the major l ipoprotein carrier is HDL, the role of these interactions on T4 entry into cells was tested first with LDL and human fibroblasts because of the well-characterized LDL receptors and the availability of cells wit h genetically absent receptors. It was shown that LDL enhanced the upt ake of T4 by cultured fibroblasts in which the LDL receptors were expr essed. The T4-binding sites on apolipoproteins B-100 and E, as well as apoA-I, have been partially characterized, and they exhibit considera ble homology. A number of possible physiologic consequences of thyroid hormone-lipoprotein interactions have been put forward as topics for further investigation.