RENAL CU AND NA EXCRETION AND HEPATIC CU METABOLISM IN BOTH CU ACCLIMATED AND NON ACCLIMATED RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Cu-64 and,, total Cu accumulation were measured in gills, plasma, live r, kidney, bile and urine during 72 h of exposure to Cu-64, at 20 mu g Cu l(-1), in non-acclimated and Cu-acclimated (28 days of pre-exposur e) rainbow trout (Oncorhynchus mykiss) fitted with urinary bladder cat heters. Renal Cu excretion gradually declined from 0.03 mu g Cu kg(-1) h(-1) in non-exposed fish to 0.01 mu g Cu kg(-1) h(-1) after 28 days of Cu exposure. A comparison of the Cu-64-labelled Cu and the total Cu excretion rates and the corresponding renal clearance revealed appare nt differences in Cu binding to plasma protein depending on whether th e Cu is derived from recent branchial uptake or is already present in the plasma prior to Cu-64 exposure. The plasma Cu pool derived from re cent branchial uptake and the Cu pool present in the plasma prior to C u-64 exposure is accessible to renal excretion to different extents, w hereas the pools seem equally accessible to hepatic accumulation and e limination. The renal Cu excretion is of minor importance compared wit h the hepatic Cu excretion, which was estimated to be 0.5-0.75 mu g Cu kg(-1) h(-1) and 1.1-1.6 mu g Cu kg(-1) h(-1) for non-acclimated and Cu-acclimated fish, respectively. Based on the biliary Cu concentratio n, hepatic Cu elimination appeared to be stimulated in the Cu-acclimat ed relative to the non-acclimated fish. Only 17% and 12% of the hepati c Cu could be accounted for by metallothionein in the control and Cu-a cclimated fish, respectively. Renal Na+ efflux decreased by 40%, which was largely due to increased tubular Na+ reabsorption. Renal compensa tion for the impaired branchial Na+ uptake, seen during Cu exposure, t hus seems to be involved in Cu acclimation in rainbow trout. (C) 1998 Elsevier Science B.V.