Effects of Zinc Deficiency per se and of Dietary Zinc Level on Urinary and Endogenous Fecal Excretion of 65Zn from a Single Intravenous Dose by Ruminants

Abstract

Following single intravenous doses of ⁶⁵Zn, rate of excretion was studied in experiments designed to separate the physiological effects of a zinc deficiency per se from those of level of dietary zinc. Fecal excretion of ⁶⁵Zn was higher in normal animals fed a normal diet containing 46 ppm zinc then in comparable animals fed a zinc-deficient diet containing 6 ppm zinc. Specific activity of fecal zinc from animals fed the deficient diet was much higher, reflecting the much lower level of total fecal zinc. When fed the same diets, normal animals excreted more ⁶⁵Zn in the feces than did zinc-deficient animals. However, the deficient animals excreted more ⁶⁵Zn in the urine, suggesting a possible pathological effect of the deficiency on the kidneys. Level of dietary zinc per se did not affect urinary excretion in normal animals. Urinary excretion of ⁶⁵Zn was highest the first day, decreased sharply the second day, and decreased gradually thereafter. Excretion of ⁶⁵Zn via urine was low, with the total for 13 days being less than 0.3% of the dose. Fecal excretion was highest the second and third days after dosing and decreased gradually thereafter. Level of ⁶⁵Zn in the blood declined very rapidly immediately following dosing and very slowly after the first day. These studies indicate that both a low zinc diet and a zinc deficiency per se cause reduced endogenous fecal excretion of ⁶⁵Zn for at least 2 weeks after the zinc enters the blood, thus contributing to homeostasis of this element.