Rate of loss of radioiron from mouse and man

¹ Mayo Clinic and Mayo Foundation, Rochester, Minnesota

Forty-two male and female mice, 8 weeks old, were given radioiron (Fe⁵⁹) in doses of 0.006–0.1 µc, containing 0.013–0.17 µg of iron, by intraperitoneal or intravenous routes. Assays of the radioactivity of the whole body revealed an initial rapid loss of Fe⁵⁹ (15–20%) lasting about 6 days. Thereafter the Fe⁵⁹ left the mice at a steady rate of 0.39%/day (half-life 180 days). One 34-year-old normal man was given 10.6 µc of Fe⁵⁹, containing 8.2 µg of iron, intravenously. Based on counts from the entire body, the biologic rate of loss of the Fe⁵⁹ was about 0.14%/day (half-life 500 days), and there was little or no initial loss such as occurred in the mouse. The Fe⁵⁹ in the circulating erythrocytes was essentially unchanged for the first 3 months. It then fell to a new level of about 90% of the previous one; the mid-point of the fall was about 120 days after the administration of the radioiron. The difference in the rates of loss of radioiron from mice and man seems to be related primarily to the life span of the circulating red cells.