Effect of acute zinc depletion on zinc homeostasis and plasma zinc kinetics in men

Background: Zinc homeostasis and normal plasma zinc concentrations are main tained over a wide range of intakes. Objective: The objective was to identify the homeostatic response to severe zinc depletion by using compartmental analysis. Design: Stable zinc isotop e tracers were administered intravenously to 5 men at baseline (12.2 mg die tary Zn/d) and after 5 wk of acute zinc depletion (0.23 mg/d). Compartmenta l modeling of zinc metabolism was performed by using tracer and mass data i n plasma, urine, and feces collected over 6-14 d. Results: The plasma zinc concentration fell 65% on average after 5 wk of zi nc depletion. The model predicted that fractional zinc absorption increased from 26% to essentially 100%. The rate constants for zinc excretion in the urine and gastrointestinal tract decreased 96% and 74%, respectively. The rate constants describing the distribution kinetics of plasma zinc did not change significantly. When zinc depletion was simulated by using an average mass model of zinc metabolism at baseline, the only change that accounted for the observed fall in plasma zinc concentration was a 60% reduction in t he rate constant for zinc release from the most slowly turning over zinc po ol. The large changes in zinc intake, excretion, and absorption-even when c onsidered together-only explained modest reductions in plasma zinc mass. Conclusion: The kinetic analysis with a compartmental model suggests that t he profound decrease in plasma zinc concentrations after 5 wk of severe zin c depletion was mainly due to a decrease in the rate of zinc release from t he most slowly turning over body zinc pool.