Evaluation of histochemical methods for the detection of copper overload in rat liver

Histochemical methods have invariably shown a good correlation with copper analysis by absorption spectrophotometry in the identification of canine copper storage diseases. But, in Wilson's disease (WD) in humans no such correlation exists and similar discrepancies have also been observed in copper-loaded rats. This study attempts to quantify stainable copper in the livers of copper-loaded rats and relate this to the hepatic copper concentrations. Male rats fed a high copper diet (1500 ppm) for 16 weeks were killed at intervals. The livers were analysed for copper and graded according to stainable copper present in paraffin sections stained with rhodanine and rubeanic acid. Initially there was a good correlation between histochemically demonstrable copper and its total concentration, but subsequently, when high liver levels of the metal were present, copper staining was very variable. This unrealiability has similarities with WD, in which the higher hepatic concentrations of presymptomatic patients are difficult to detect by conventional copper stains. The variation in the binding of copper and its intracellular localisation suggested by these results may have considerable significance in the pathogenesis of copper storage diseases.