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Experimental evaluation of the vascular effects and transport of an iodinated macromolecular contrast medium.

RATIONALE AND OBJECTIVES
For assessment of the tissue blood pool and overall vascularity, macromolecular contrast media have significant advantages over low molecular weight contrast agents. The authors evaluated the vascular effect and transport of a new macromolecular contrast media (MMCM), an iodinated dextran polymer of 32 kDa.


METHODS
The new MMCM was obtained from dextran activated by carboxy methylation, followed by linkage with triiodinated aminophtalamid conjugates. To detect whether the tracer induces vascular leakage, MMCM (350 mg I/kg) was administered intravenously in 10 mice, or applied on the cremaster muscle of 26 mice previously injected with carbon particles; after 30 or 45 minutes, the cremaster was fixed and examined by optical microscopy. For investigation of the vascular transport 3, 5, and 15 minutes after MMCM administration, various tissue fragments were processed and examined by electron microscopy.


RESULTS
In all vascular examined, MMCM does not induce plasma extravasation and the probe was detected mostly within the vascular lumen. At the ultrastructural level, a small fraction of MMCM was found in endothelial plasmalemmal vesicles (endosome-like structures) and, in time, transcytosed to the subendothelial space. No intercellular junctions were permeated by MMCM.


CONCLUSIONS
The MMCM induces no vascular leakage and it is retained mainly in the plasma. Transport of MMCM is restricted to endothelial vesicles, which may explain, in part, its prolonged vascular space retention.