Abstract
Mice were given tritiated water (HTO) to drink for 40-147 days at a specific activity of 94 ± 4.8 μCi/ml (mean ± SD). Tissue HTO was 77.8 ± 10.1 μCi/ml in liver, testis and intestinal mucosa, reflecting the input of H2 O in unlabeled food and metabolic H2 O. Bound T specific activity was 15.8 ± 6.0 μCi/g dry matter. Kangaroo rats (Dipodomys merriami) were given periodic HTO injections and fed a dry diet, with similar results. In both species the specific activity of nonaqueous tissue hydrogens was 25-40% that of hydrogen in tissue HTO. The total soft tissue radiation dose was estimated to be over 2000 rads. In the mouse nonexchangeable T in liver DNA had a specific activity 12% that of hydrogen in tissue HTO; and all four bases were labeled. An apparent tritium isotope effect was observed in the lungs. The specific activity of expired HTO vapor relative to tissue HTO was 0.44 in kangaroo rats and 0.64 in mice.
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