Localization of cytochrome P-450 in the head and trunk kidney of rainbow trout ( Salmo gairdneri)

Abstract

Mature, untreated rainbow trout display a marked sex difference in the level and activity of the P-450-dependent mixed-function oxidase system with males demonstrating higher levels than females. This difference is accentuated in the trunk kidney, is specific for endogenous substrates such as lauric acid and sex steroids, and is correlated with greater levels of the constitutive cytochrome P-450 isozyme, LM 2. Using an immunohistochemical technique, the cellular localization of P-450 LM 2 and P-450 LM 4b, the major β-naphthoflavone inducible isozyme, in the head and trunk kidney of male, female, and juvenile trout has been demonstrated. Immunostaining for P-450 LM 2 was observed in the cytoplasm of cells in the second portion (P 2) of the proximal tubules of both male and female trout. In male fish, staining appeared to be more intense and involved most of the P 2 segments in a tissue section. In female fish, P 2 staining was moderate and involved fewer segments. Low staining intensity for P-450 LM 4b was observed in the cytoplasm of cells both in the first portion of the proximal tubules and in P 2 of male and female fish. Sexual dimorphism was not apparent. The finding of greater amounts of P-450 LM 2 in males and low levels of P-450 LM 4b in untreated male and female trout confirms previous biochemical studies. Localization of P-450 isozymes in the proximal tubules is consistent with findings in mammalian species. Moderate immunostaining by anti- P-450 LM 4b IgG also was observed in the interrenal cells of the head kidney of male, female, and juvenile trout.