Abstract
The double-labeled lipid microspheres with 3H-dipalmitoylphosphatidylcholine (DPPC) and 14C-tripalmitin (TP) having various particle sizes : small ; 50 nm, medium ; 130 nm, large ; 215 nm in mean diameters, were prepared by a Microfluidics homogenizer. After intravenous administration of microspheres to rats, plasma levels of radioactivities were measured from 1 to 360 min periodically. The smaller the particle size of lipid microsphere was, the faster the elimination of radioactivities from plasma was ; which was contrary to the results of liposomes. Elimination of 14C-TP from plasma was faster than that of 3H-DPPC in any microspheres, particularly in small and medium microspheres. This result suggested that triglyceride in microsphere core was hydrolysed and eliminated from circulation, while phospholipid was remained in the surface lipid monolayer of microsphere. Sucrose step-density gradient fractionation of the rat plasma samples showed that a large part of the radioactivity moved to the high-density fraction from the low-density (microshere's) fraction. The transported radioactivity of 14C was much in the smaller microsheres. These results suggested that clearance of microsphere from plasma was much influenced by the interaction with apoproteins and lipases rather than the uptake by reticuloendotherial system. A part of this work was supported by a grant from Human Science Foundation
