Competition between copper and silver in Fischer rats with a normal copper metabolism and in Long-Evans Cinnamon rats with an abnormal copper metabolism

Abstract.

Long-Evans Cinnamon (LEC) rats inherently lacking in serum ceruloplasmin (CP) activity and biliary Cu excretion were established from a closed colony of Long-Evans rats. These deficiencies, linked to a dysfunction of P-type ATPase, stimulate deposition of Cu and then of Cu metallothionein (MT) in the liver. Male LEC and Fischer rats were injected subcutaneously with Ag (AgNO₃), which is an antagonist to Cu. They were operated on 24 h after the injection while under anesthesia. Total uptake of Ag into the liver was not stimulated, but its uptake into the MT fraction increased significantly in the LEC rats. Ag injection notably decreased the activity of serum CP in the Fischer rats, but not in the LEC rats. The decrease was accompanied by a reduction of serum Cu. In Fischer rat serum treated with Ag, Ag was detected mainly in the albumin region and partly in the CP fraction. In LEC rat serum, however, the Ag concentration was about 1/20 of that in the Fischer rats, and Ag was not detected in the CP fraction. Ag injection decreased the biliary excretion of Cu in the Fischer rats (0.183–0.052 µg Cu/20 min sampling), but not in the LEC rats (0.014–0.014 µg Cu/20 min sampling). On the other hand, biliary excretion of Ag was much greater in the Fischer rats (1.25 µg Ag/20 min) than in the LEC rats (0.04 µg Ag/20 min). Our results suggest that uptake of Ag into the liver is not dependent on the hepatic Cu content and status, but that biliary excretion of Ag from the liver is affected by these. Hepatic MT is not a transporter of hepatobiliary excretion of Cu and Ag. It seems likely that, unlike Cu excretion, Ag is excreted by not only the CP route but also by another route into the serum. Ag may compete with Cu in the uptake into CP (conversion of apo-CP to holo-CP).