Tissue distribution of high-density lipoprotein labeled with radioiodinated cholesterol

This preliminary study was undertaken in order to explore possible methods for enhancing the target organ specificity of radioiodinated cholesterol. 19-[125I]cholesterol (IC) was rapidly incorporated and transported in high-density lipoproteins (HDL) following i.v. admnistration to rats, and thus behaved like cholesterol in this regard. Incorporation of IC into HDL (IC-HDL) before administration produced little change in the tissue distribution profile except for a reduction in the amount of radioactivity appearing in the thyroid. This suggested that the lipoprotein carrier may have afforded protection from metabolic dehalogenation of IC. When rats were pretreated with 4-aminopyrazolo-(3,4d)-pyrimidine to drastically reduce the circulating lipoprotein levels, a fourfold enhancement in adrenal uptake was observed following administration of IC-HDL. This finding was consistent with the current view that the rat adrenal contains high-affinity and saturable receptors for HDL.