TESTICULAR TOXICITY OF THE TRANSFERRIN-BINDING RADIONUCLIDE IN-114M IN ADULT AND NEONATAL RATS

Adult (70 d) and neonatal (7 d) male rats were dosed (i.p.) with 37 MB q/kg (1 mCi/kg; approximately 1 mu g elemental indium/kg) In-114m, a t ransferrin-binding radionuclide. In adults, approximately 0.25% of the injected activity localised within the testis by 48 h postinjection a nd remained constant for up to 63 d. In neonates, 0.06% of the activit y was in the testis by 48 h, and this declined such that by 63 d only 0.03% remained. At 63 d, treated rats had reduced sperm head counts an d abnormal testicular histology that was more marked in animals dosed as adults than as neonates. In vitro, uptake of In-114m into seminifer ous tubules isolated from 7-, 20-, or 70-d-old rats was compared with that of I-125. Both radionuclides were readily accumulated by the tubu les. Whilst In-114m uptake into 20- and 70-d tubules was inhibited by excess transferrin, uptake into 7-d tubules was unchanged. I-125 uptak e was not affected by excess transferrin. These data support the conte ntion that some radionuclides may cross the blood-testis barrier by ut ilisation of the physiologic iron-transferrin pathway, which may lead to greater testicular damage in adult compared to neonatal animals.