INDUCTION OF METALLOTHIONEIN GENE-EXPRESSION BY CADMIUM AND THE RETENTION OF THE TOXIC METAL IN THE TISSUES OF RAINBOW-TROUT (SALMO-GAIRDNERI)

1. When rainbow trout were exposed to cadmium by intraperitoneal injection, there was a rapid (within 3 hr) and significant (approx. 63%) loss of the metal from the whole bodies of the fish. 2. Of the metal retained in the bodies of the fish (approx. 37% of the injected dose), more than 98% was accounted for collectively among the liver, kidney and gills. 3. Subsequent maintenance of the rainbow trout in fresh water for up to 98 days post-metal administration, indicated that there was no further loss of the cadmium accumulated in the organs studied and that the distribution of the metal among the liver, kidney and gills remained unchanged over that period. 4. During this 98-day period of maintenance of the fish, tissue concentrations of metallothionein-specific mRNA and metallothionein protein were quantified using riboprobe and ELISA systems respectively. Metallothionein-specific mRNA concentrations increased rapidly (within 24 hr) before falling back to levels similar to, or slightly greater than, those found in control animals. The concentration of metallothionein protein also increased significantly (within 3 days) then remained elevated thereafter. 5. Throughout the experimental period, the concentrations of zinc and copper were also monitored in the liver, kidney and gills of the rainbow trout. The concentrations of each ion differed between each of the organs but did not change during the experiment. 6. The induction of metallothionein gene expression by cadmium in the liver, kidney and gill of rainbow trout and the subsequent sequestration of the toxic metal is discussed with regard to the relative levels of these other essential metal ions.