Tissue distribution, kinetics, and biologic half-life of Mg²⁸ in the dog

¹ Department of Medicine, Tulane University School of Medicine, and Charity Hospital of Louisiana, New Orleans, Louisiana

Mg²⁸ of a high specific activity was used in these studies. It was rapidly injected intravenously into 12 dogs and the concentration-time course curves in plasma were obtained. Urinary and fecal excretion was followed in seven animals. The dogs were killed 7 min to 68 hr following injection. Seventy-four tissues were sampled and assayed for Mg²⁸ concentration. Plasma Mg²⁴ was determined by flame spectrophotometry. With these data it was possible to follow the concentration-time course of Mg²⁸ in the various tissues as well as to calculate their "exchanging" Mg²⁴ content and effective rates of exchange. A variation in the pattern of uptake and in concentration of exchanging Mg²⁴ was noted among the different tissues. During the interval from 24–68 hr, body exchanging Mg²⁴ space and mass were found to range from 3.2–3.8 liters/kg and 4.9–5.7 mEq/kg, respectively. The biologic half-life of Mg²⁸ in the dog estimated from excretion data was 11 days.