A turnover study in the male rat of plasma-bound 59Fe, 114Inm and 109Cd with particular reference to the gonad.

After intravenous doses of the plasma-bound radionuclides 59 Fe, 114 In m and 109 Cd, 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 percentage retention of 14, 65 and 11 for 59 Fe, 114 In m and 109 Cd, respectively. By this route, significant feedback of the elements escaping initial binding was prevented. Distinct but different testicular turnovers 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 59 Fe no measurable changes were detected, whereas a progressive increase in epididymal 114 In m occurred, which had not reached a plateau by 70 days. 109 Cd, now demonstrated within the testicular tubules by autoradiography, remained at constant organ level for upwards of 16 days but had declined by 25% by 57 days. At this point, the epididymis showed a five-fold increase in the radionuclide, declining to one-half this value by 126 days. Since 109 Cd is carrier free, the data reflect a body turnover of dietary cadmium. These results, overall, are compatible with the entry of a proportion of each radionuclide into the seminiferous tubules and reaction with spermatogenic cells. Possible interpretations of the observed differences are presented