Whole-body retention and gastrointestinal absorption of $sup 106$Ru and $sup 144$Ce in suckling mice

Suckling mice of various ages were administered orally a single dose of / sup 106/Ru or /sup 144/Ce to investigate the whole-body retention and gastrointestinal absorption of these radioactive substances. The younger the suckling mice, the higher was the retention and the longer the biological half- time of /sup 106/Ru. When mice approached the weaning time, the retention curve of /sup 106/Ru decreased sharply to a level of 1 to 2% of the dose and then slowly thereafter. Around seven per cent of the dose of /sup 106/Ru was absorbed from the gastrointestinal tract in 0-day-old mice for 24 hours after administration. This value decreased to about 0.8% of the dose over a period from 1 day to 4 weeks after administration. Also in the case of /sup 144/Ce, the younger the mice, the higher was the wholebody retention and the better the intestinal absorption. The net absorption, which was estimated in 0-day-old mice, from 4% of the dose 1 day after administration to 28% of the dose 3 weeks after administration. (auth)