A TURNOVER STUDY IN THE MALE-RAT OF PLASMA-BOUND FE-59, IN-114(M) ANDCD-109 WITH PARTICULAR REFERENCE TO THE GONAD

After intravenous doses of the plasma-bound radionuclides Fe-59, In-11 4(m) and Cd-109, only a minute percentage localizes in the rat testis and remains largely unchanged with time. Intratesticular injection of appropriately reduced volumes led to much higher proportionate percent age retention of 14, 65 and 11 for Fe-59, In-114(m) and Cd-109, respec tively. By this route, significant feedback of the elements escaping i nitial binding was prevented. Distinct but different testicular turnov ers were now discernible. As a receptor of fluid and spermatozoa from the testicular tubules, the epididymis provides an indication of entry into and interaction of the metals with spermatogenic cells. For Fe-5 9 no measurable changes were detected, whereas a progressive increase in epididymal In-114(m) occurred, which had not reached a plateau by 7 0 days. Cd-109, now demonstrated within the testicular tubules by auto radiography, remained at constant organ level for upwards of 16 days b ut had declined by 25% by 57 days. At this point, the epididymis showe d a five-fold increase in the radionuclide, declining to one-half this value by 126 days. Since Cd-109 is carrier free, the data reflect a b ody turnover of dietary cadmium. These results, overall, are compatibl e with the entry of a proportion of each radionuclide into the seminif erous tubules and reaction with spermatogenic cells. Possible interpre tations of the observed differences are presented.