Influence of heavy metals upon the retention and mobilization of polonium‐210 in rats

Abstract

Purpose: To provide information about the tissue retention and mobilization of the alpha‐emitting radionuclide, polonium‐210 (²¹⁰Po), in rats under combined exposure to heavy metal ions and the chelating agent, 2, 3‐dimercaptopropane‐1‐sulfonate (DMPS).

Materials and methods: Rats were pre‐exposed intraperitoneally to either CdCl₂ or Pb(CH₃COO)₂. 9 or 15 h later they received ²¹⁰Po nitrate intravenously. The retention and excretion of ²¹⁰Po via the urine and faeces of pre‐exposed rats, as well as in pre‐exposed rats treated with DMPS, were followed. The radioactivity due to ²¹⁰Po in a broad spectrum of body tissues and excreta was measured by the liquid scintillation counting after sample digestion in a mixture of perchloric acid and hydrogen peroxide. The immunohistochemical localization of metallothioneins (MT) was studied using a mixture of murine monoclonal antibodies directed against MT I+II.

Results: The present study revealed different tissue distributions of polonium‐210 in the rats pre‐exposed to lead or cadmium ions when compared with that in ²¹⁰Po only controls. Under combined exposure to Pb or Cd, the spontaneous excretion of ²¹⁰Po was enhanced and could be further enhanced by treatment with DMPS. Treatment with this chelator was efficient even when its start was postponed until 24h after internal contamination of the body with ²¹⁰Po.

Conclusions: Polonium‐210 is bound in vivo to binding sites on various biomolecules, among them erythrocytic enzymes and MT. This phenomenon explains the different affinity and overall distribution of ²¹⁰Po in control body tissues. When the appropriate binding sites are occupied by lead or cadmium, enhanced natural excretion of polonium‐210 occurs.