AN INVESTIGATION OF THE EFFECT OF LONG-CONTINUED INGESTION OF ZINC, IN THE FORM OF ZINC OXIDE, BY CATS AND DOGS, TOGETHER WITH OBSERVATIONS UPON THE EXCRETION AND THE STORAGE OF ZINC
Cats and dogs were fed with daily doses of ZnO of 175-1000 mgm. for 3-53 weeks. No significant clinical symptom or any significant laboratory evidence of damage was ever observed. With the exception of fibrous change in the pancreas of 3 cats subjected to doses of Zn very greatly in excess of any possible human exposure, histological examination following autopsy showed in organs of zinced cats and dogs no damage of any sort attributable to Zn. The normal amount of Zn excreted daily in cat urine was 0.06-0.43 mgm.; in dog urine, 0.13-0.59 mgm.; in dog feces, 5.0-25.0 mgm. In Zn-fed animals a small fraction of absorbed Zn apparently leaves the body in the urine, but the main bulk is excreted into the alimentary tract[long dash]some directly, some by the liver into the bile, and possibly some by the pancreas[long dash]and ultimately leaves the body in the feces. The amount of Zn in the urine of Zn-fed animals was markedly increased over the normal, though the total amount was but a small fraction of the total excreted. Animals excreted abnormal amounts of Zn through the kidneys for months without histological evidence of kidney damage. Data presented on normal Zn concentrations in tissues and[long dash]1023[long dash]organs of cats and dogs, in tissues and organs of zinced animals, and of zinced animals in which Zn administration had been discontinued for 2 weeks, indicate that the Zn concentrations of organs involved in excretion of Zn (liver, gall bladder and bile, gastrointestinal tract, and kidney) are increased as a result of ZnO ingestion, but that these abnormal concentrations fall rapidly to normal when Zn dosing is discontinued. Zn concentrations in bone, bone marrow, and pancreas are also increased by Zn feeding[long dash]increases which fall towards the normal level on discontinuance of Zn. A possible excretory function of the pancreas is suggested in this connection. Total Zn concentration of Zn-fed animals increased slightly with moderate Zn dosing and somewhat more markedly with excessive dosing, but fell practically to normal within 2 weeks after Zn dosing was discontinued. A possible connection is suggested between the Zn content and the functional activity of the adrenals and sex glands.