Urinary zinc excretion following infusions of zinc sulfate, cysteine, histidine, or glycine.

Zinc sulfate (40 mg elemental zinc) or one of three amino acids (5 or 10 g cysteine, 10 g histidine, or 10 g glycine) was infused into anesthetized dogs over a 60-min period. Plasma concentrations and urine excretions of zinc and five other cations, and glomerular filtration rates were determined before, during, and after these infusions. Infusions of zinc sufficient to produce a 20-fold increase in total plasma zinc concentrations had little effect on urinary zinc excretions (threefold increase) or plasma ultrafilterable zinc concentrations. Ten grams of cysteine urinary zinc excretions more than 100-fold, 5 g of cysteine increased zinc excretions more than 30-fold, 10 g of histidine increased zinc excretions sixfold, and 10 g of glycine had no effect. Cysteine infusions appeared to produce a net tubular secretion of zinc. Only histidine appeared to increase serum ultrafilterable zinc concentrations significantly. It would appear that plasma and urine concentrations of certain amino acids, specifically cysteine and histidine, along with polypeptides and other metabolites containing these amino acids, may be major determinants of urinary zinc excretion.