Studies on zinc in blood. Transport of zinc and incorporation of zinc in leucocytes

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Abstract
The transport of zinc in the blood of the rabbit after the intravenous injection of zinc-glycine solutions, and the rate of removal of the metal from the blood, have been studied with Zn65 as tracer. The injected zinc was rapidly removed from blood and about 90% left the blood stream in the course of 3 hr. A similar rapid loss occurred when plasma labelled in vivo with Zn65 was injected. Plasma protein-bound zinc is thus readily exchangeable with the pool of body zinc. The blood plasma of the rabbits, 3-24 hr. after the injection of zinc-glycine, contained essentially all its Zn65 in a bound form. About half this zinc was attached to the plasma globulin, and it has been shown that the a-globulin fraction is responsible for the carriage of the main part of the zinc. Dialysis studies have shown that at pH 7-4 all the zinc is removed from rabbit plasma by ethylenediaminetetra-acetic acid, but only a small fraction (about 7%) by glycine. Intravenous injection of iron salts into rabbits in amounts sufficient to saturate the iron-carrying capacity of the plasma proteins has no significant effect on the binding powers of plasma for zinc in vivo. It has been confirmed that the zinc-binding capacity of rabbit leucocytes is very much greater than that of the erythrocytes. Ratios of leucocyte Zn65 to erythrocyte Zn65 in blood and bone marrow 24 hr. after the injection of zinc-glycine containing Zn65 were 39-75/1 and 30/1 respectively. Studies have shown that in vitro there is a rapid exchange of zinc between erythrocytes and plasma, with no detectable transference of zinc from leucocytes to plasma. Uptake of zinc by leucocytes from plasma is rapid. The role of the blood cells in the transport and storage of zinc in the blood cells, mainly that in the erythrocytes, should be regarded as a significant part of the mobilizable or "available" zinc in the animal body.