Cysteine feeding affects urinary zinc excretion in normal and ethanol-treated rats

The effects of L-cysteine feeding on urinary zinc excretion were studied in normal and ethanol-treated rats. In rats fed 3% cysteine X HCl for 1-10 weeks, a three-fold increase of urinary zinc excretion was observed. That effect was variable but was significant throughout the experimental weeks. Despite the excessive zinc loss, cysteine-fed animals showed no evidence of zinc depletion as judged by zinc concentrations in plasma, hair, spleen, pancreas and muscle. Furthermore, zinc contents in liver, kidney and tibia were significantly higher in cysteine-fed rats than in their controls. In rats consuming 20% ethanol for 5 months, urinary excretion of magnesium was markedly elevated and of zinc, only slightly elevated. When rats that drank either 20% ethanol or an isocaloric sucrose solution were fed the cysteine-fortified diet, elevations of urinary zinc excretion were similar. Cysteine intake apparently did not affect urinary excretion of copper and magnesium. Diets supplemented with DL-ethionine or L-cystine, but not inorganic sulfate, methionine or ascorbic acid, induced minor elevation of urinary zinc output. Those findings suggest that cysteine has a specific role in zinc metabolism.