The effect of scandium on the tissue distribution of Ga-67 in normal and tumor-bearing rodents.

In rats and mice the intravenous administration of scandium before or with Ga-67 produces an increase in Ga-67 excretion and bone deposition, coupled with pronounced decreases in the uptake of Ga-67 in soft tissues. These effects result from the blocking by scandium of Ga-67 plasma-protein binding sites, which forces Ga-67 into an unbound or loosely bound state. This increases Ga-67 excretion and bone deposition, which in turn acts to produce greatly reduced Ga-67 uptake in soft tissues. When tumor-bearing rats and mice are administered scandium, similar effects occur, but the uptake of Ga-67 by tumor tissue remains unchanged. This suggests that Ga-67 enters tumor and normal soft tissues by different routes. With tumor, an unbound or loosely bound form of gallium is primarily involved, whereas with normal soft tissues this route is apparently of minor importance.