In vitro hydroxylation of vitamin D-3 and 25-hydroxy vitamin D-3 in tissues of Atlantic salmon Salmo salar, Atlantic mackerel Scomber scombrus, Atlantic halibut Hippoglossus hippoglossus and Atlantic cod Gadus morhua

The in vitro metabolism of (CD3)-C-14 and (3)H25OHD(3) was investigated in different tissues from Atlantic salmon Salmo salar, Atlantic mackerel Scomb er scombrus, Atlantic halibut Hippoglossus hippoglossus and Atlantic cod Ga dus morhua. The tissues analysed were liver, kidney, head kidney, gills, sp leen and intestine. The metabolites were extracted in methanol-chloroform a nd separated by normal-phase high-pressure liquid chromatography (HPLC) fol lowed by scintillation counting. Identification of the metabolites was by c omigration with standards on normal and reversed-phase HPLC systems and by protein-binding assays. All tissues from all species analysed produced hydr oxylated derivatives identified as 25OHD(3), 24,25(OH)(2)D-3 and 1,25(OH)(2 )D-3. In addition, some unidentified derivatives were recorded, one probabl y being 25,26(OH)(2)D-3. Organs producing great amounts of one metabolite a lso produced considerable amounts of the other possible derivatives, sugges ting a lower degree of specificity in fish organs than in human organs. The predominating metabolite was 24,25(OH)(2)D-3 in all organs from salmon and mackerel during incubation with (CD3)-C-14 and within most organs from all species during (3)H25OHD(3) incubation. The latter observation probably re sults from the need for decreasing rather than increasing the calcium absor ption in these species, which live at least some periods of life in a marin e environment.