Absorption and Tissue Distribution of Radiozinc in Steers Fed High-Zinc Rations

Abstract

Radiochemical procedures have been employed to study the movement of zinc through the body of four yearling steers. Absorption and tissue distribution in two steers maintained for more than a year on 1000 ppm. zinc were compared with control animals following oral and intravenous administration of the radioisotope. Concurrent chemical and radiozinc balance studies indicated that most of the zinc was excreted in the feces and was not absorbed. Those steers dosed orally with zinc⁶⁵ excreted 72.2 and 65.8 percent in the feces and 0.24 and 0.39 percent in the urine on the high-zinc and control rations, respectively. Following intravenous administration, 20.6 and 0.25 percent of the dose was excreted in the feces and urine, respectively, with no differences attributable to dietary zinc level noted. The rate of disappearance of zinc⁶⁵ from the blood following intravenous administration resulted in the attainment of equilibrium between blood and soft tissue in 10 hours. The partition between plasma and cells presented as a function of time indicated that equilibrium between the two fractions occurred at about 6 hours, after which activity in the red cells predominated. The accumulation of retained radiozinc was, in general, highest in the soft tissue, the pancreas, liver, pituitary, kidney and adrenals having highest concentration. Turnover rate was highest for the liver and lowest for the incisor teeth. The accumulation and turnover of zinc in the various bones paralleled their metabolic activity.