Age dependence of excretion and tissue distribution of tritium after single oral administration of tritiated water to rats of various ages.

Tritiated water was given to rats of various ages through a stomach tube. For the excretion study urine sample was collected periodically and its tritium concentration was determined with a liquid scintillation counter. The result showed clearly that the tritium metabolism depends on the age of the animal. The general trend was that the older the animal the longer the biological half life of tritium. The exception of this was the slightly longer biological half life for sucklings than that of weanlings. For tissue distribution study, experimental animals were sacrificed periodically after administration of tritiated water. Tritium incorporation was assessed both in the aqueous fraction and in the organic component of tissues from various organs, including the blood, brain, liver, muscle and testis. During the first several days after administration the tritium concentration in the tissue water decreased rapidly while that in the tissue organic matter decreased more slowly. This was more notable in the younger animals. In the weanlings, the tritium concetration became lower in the tissue water than in the tissue organic matter about 12 days of postadministration in contrast to the 24 days in the adult rat.