Radioactive dextran particles for studying circulation in animals.

Two types of dextran particles, (density 1.12 g X cm-3), ie chelating dextran particles (diameters 15.0 and 52.0 microns) and Sephadex (diameter 49.5 microns) were prepared for use as radioactive microspheres after labelling with 57Co, 58Co or 131I. The labelling efficiency was 96.4% with 57Co or 58Co and 7.8% with 131I. The specific activities were in the range 1 to 60 microCi X mg-1. The dissociation of cobalt label was found to be negligible in vitro, and in vivo 0.4 to 0.7% per h. Most of this activity was rapidly excreted in the urine. 35 days after injection of 15 microns particles they were still entrapped in the lungs and had undergone no microscopic changes and caused no tissue reaction. The findings validate the use of cobalt labelled particles for animal experiments of several hours duration. The dissociation of the iodine label was considerable both in vitro and in vivo limiting the use of the iodine labelled particles to experiments where a single determination of blood flow distribution is sufficient.