Virtual absence of turnover in cadmium metabolism: Cd109 studies in the mouse

Abstract

Following injection, radioisotopes of physiologically occurring elements are excreted at rates that increase upon metabolic loading with stable carrier. In contrast, Cd109 showed negligible total-body turnover in the mouse regardless of challenges with Cd or Zn, and alimentary absorption occurred irrespective of the body's Cd burden. As opposed to certain bone-seeking nonphysiological radioisotopes which also show this behavior, Cd109 concentrated primarily in nonosseous soft tissue. Intracellularly the distribution of Cd109 resembled that of Zn65, except for a lower uptake of Cd109 by the nuclear fraction. Other dissimilarities between Cd and Zn metabolism included the presence of a well-defined excretory pathway only for Zn and different effects of Cd and Zn carriers upon the organ distribution of Cd109. These findings suggest the following: a) Cd does not obey homeostatic control; b) similarities between Cd and Zn metabolism imply that Cd may function, in part, as an antimetabolite of Zn; c) significant physiological discrimination between Cd and Zn exists, at least at the level of excretory processes.