We have previously shown that (1) an acute deficiency in blood
serum holo-ceruloplasmin (Cp) developed in rats that were fed fodder containing
silver ions (Ag-fodder) for one month and (2) the deficiency in
holo-Cp was compensated by non-hepatic holo-Cp synthesis in rats that were
chronically fed Ag-fodder for 6 months (Ag-rats). The purpose of the present
study is to identify the organ(s) that compensate for the hepatic holo-Cp
deficiency in the circulation. This study was performed on rats that were fed
Ag-fodder (40 mg Ag·kg-1 body mass daily) for 6 months. The relative
expression levels of the genes responsible for copper status were measured by
RT-PCR. The in vitro synthesis and secretion of
[14C]Cp were analyzed using a metabolic labeling approach. Oxidase
activity was determined using a gel assay with o-dianisidine.
Copper status and some hematological indexes were measured. Differential
centrifugation, immunoblotting, immunoelectrophoresis, and atomic absorption
spectrometry were included in the investigation. In the Ag-rats, silver
accumulation was tissue-specific. Skeletal muscles and internal (IAT) and
subcutaneous (SAT) adipose tissues did not accumulate silver significantly. In
SAT, the mRNAs for the soluble and glycosylphosphatidylinositol-anchored
ceruloplasmin isoforms were expressed, and their relative levels were increased
two-fold in the Ag-rats. In parallel, the levels of the genes responsible for Cp
metallation (Ctr1 and Atp7a/b) increased
correspondingly. In the SAT of the Ag-rats, Cp oxidase activity was observed in
the Golgi complex and plasma membrane. Moreover, full-length [14C]Cp
polypeptides were released into the medium by slices of SAT. The possibilities
that SAT is part of a system that controls the copper balance in mammals, and it
plays a significant role in supporting copper homeostasis throughout the body
are discussed.