Tetracycline Accelerates Elimination of Strontium from Bones in Mice. ∗

Abstract

The antibiotic tetracycline, identified in tissues by its golden fluorescence, is preferentially deposited in growing bone(1), and has been shown to inhibit skeletal formation in the chick embryo(2). It has been hypothesized that the tetracyclines interfere with cellular and enzymatic processes by virtue of their affinity for inorganic cations, especially calcium and magnesium(3). We have investigated the effects of tetracycline on strontium metabolism in adult mice, using Sr-85, a gamma emitter, as tracer. Aside from its importance in radioactive fallout (as the isotope Sr-90), strontium has gained increasing attention as a tracer for studying bone metabolism, being handled in the body qualitatively similarly to calcium(4).

In this experiment, 19 Swiss Webster mice were given single injections of Sr⁸⁵(NO₃)₂, 1 μC each, specific activity 200 μ/mg. The control group, consisting of 10 animals, received no other treatment. The 9 mice in the second group were given daily injections of tetracycline, 150 mg/kg, starting on the 4th day prior to Sr-85 injection, and continuing to the 25th day after Sr-85 injection, when all the animals were sacrificed. The amount of Sr-85 in each mouse each day was measured with an external gamma detector (NaI scintillation counter). Average values of total body Sr-85 against time are shown in Fig. 1. Each curve has a fast component, representing direct excretion from the body of a portion of the initial dose, and a slower component, representing gradual elimination of the portion incorporated into bone. Extrapolation of the slow exponential yields the fraction of the original dose which was deposited in bone. At autopsy, no significant Sr-85 was present in any tissue except bone. The Sr-85 content of femurs from each mouse was determined. Comparision of the two group averages (± S.D.) is set forth below.