Effects of histidine on tissue zinc distribution in rats

Histidine has been reported to affect body zinc status by increasing urinary zinc excretion. The effects of experimental histidinemia on distribution of⁶⁵Zn in anesthetized rats were studied. Infusion ofl-histidine at a rate sufficient to raise plasma concentrations to approximately 2mm for 6h starting 48 h after a single intraperitoneal⁶⁵Zn injection did not alter⁶⁵Zn activities in a variety of tissues when compared with anesthetized uninfused animals. However, plasma⁶⁵Zn and erythrocyte⁶⁵Zn were decreased, and liver⁶⁵Zn was increased. If⁶⁵Zn was injected intravenously during histidine infusion, net accumulation of zinc by some tissues was increased, but uptake by others was reduced relative to uninfused animals. In all cases, however, uptake expressed relative to plasma⁶⁵Zn levels was increased when allowance was made for the more rapid fall in plasma⁶⁵Zn during histidine infusion. Similar infusions ofd-histidine produced quantitatively similar effects. Since enzymatic mechanisms and amino acid carriers would be expected to show stereoselectivity, such processes are unlikely to be involved in the zinc distribution changes described. The possibility of zinc transport by a hitherto unidentified carrier is discussed. These experiments confirm that histidinemia can affect zinc status, but any associated changes in urinary zinc excretion do not seem adequate to account for the tissue changes found.