Imaging of hepatic low density lipoprotein receptors by radionuclide scintiscanning in vivo.

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Abstract
The low density lipoprotein (LDL) receptor mediates the cellular uptake of plasma lipoproteins that are derived from very low density lipoproteins (VLDL). Most of the functional LDL receptors in the body are located in the liver. Here, a radionuclide scintiscanning technique is described that permits the measurement of LDL receptors in the livers of intact rabbits. 123I-labeled VLDL were administered i.v., and scintigraphic images of the liver and heart were obtained at intervals thereafter. In 7 normal rabbits, radioactivity in the liver increased progressively between 1 and 20 min after injection, while radioactivity in the heart (reflecting that in plasma) decreased concomitantly. In Watanabe-heritable hyperlipidemic rabbits, which lack LDL receptors on a genetic basis, there was little uptake of 123I-labeled VLDL into the liver and little decrease in carediac radioactivity during this interval. The LDL receptor is necessary for the hepatic uptake of VLDL-derived lipoporoteins in the rabbit. Two conditions that diminish hepatic LDL receptor activity, cholesterol-feeding and prolonged fasting, also reduced the uptake of 123I-labeled VLDL in the liver as measured by scintiscanning. Radionuclide scintiscanning can be used as a noninvasive method to quantify the number of LDL receptors expressed in the liver in vivo.

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