Distribution of iodine into blood components of the sprague‐dawley rat differs with the chemical form administered

Abstract

It has been reported previously that radioactivity derived from iodine distributes differently in the Sprague‐Dawley rat depending on the chemical form administered (Thrall and Bull, 1990). In the present communication we report the differential distribution of radioactivity derived from iodine (l₂) and iodide (l⁻) into blood components. Twice as much radioiodine is in the form of l⁻ in the plasma of animals treated with ¹²⁵I⁻ compared to ¹²⁵l₂‐treated rats. No l₂ could be detected in the plasma. With an increase in dose, increasing amounts of radioactivity derived from ¹²⁵l₂‐treated animals distribute to whole blood compared to equivalent doses of ⁷²⁵/⁻, reaching a maxima at a dose of 15.8 μmol I/kg body weight. Most of the radioactivity derived from l₂ associates with serum proteins and lipids, in particular with albumin and cholesteryl iodide. These data indicate a differential distribution of radioactivity depending on whether it is administered as iodide or iodine. This is inconsistent with the commonly held view that iodine (l₂) is reduced to iodide (l⁻ before it is absorbed systemically from the gastrointestinal tract.