title: Age-dependent in situ hepatic and gill CYP1A activity in the see-through medaka (Oryzias latipes).
abstract: We used a recently introduced strain of medaka, the see-through medaka, whose internal organs can be seen through the skin, to develop an in situ toxicity assay of ethoxyresorufin-O-deethylase (EROD) activity that detected fluorescence from resorufin, a metabolite of ethoxyresorufin and thus an indicator of CYP1A activity. EROD activity in the liver and gills of 2-week post-hatch see-through medaka exposed simultaneously to various concentrations of 3-methylcholanthrene and 200 microg/L ethoxyresorufin for 24 h was proportional to the 3-methylcholanthrene dose. Activities in the liver and gills peaked at 40 microg/L of 3-methylcholanthrene and then decreased at higher doses, possibly because of 3-methylcholanthrene toxicity. At 1-week post-hatch stage, however, constant high EROD activity was observed in controls and at all 3-methylcholanthrene doses. Four-week post-hatch see-through medaka exhibited less EROD activity than 2-week post-hatch see-through medaka, and activity in the liver peaked at 100 microg/L of 3-methylcholanthrene. Adult see-through medaka were not suitable for fluorescence detection owing to their thick skin, muscle and/or tissue. In tests of oxidative activity response to ethoxyresorufin, 1-day and 1-week post-hatch see-through medaka exhibited high intrinsic EROD activity in the liver, gills, and other organs in the absence of 3-methylcholanthrene. This intrinsic activity declined with growth and explained the high constant EROD activity at 1-week post-hatch stage.
authors.affiliation: National Institute for Environmental Studies, Tsukuba, Japan. shosaku@nies.go.jp
authors.forename: Shosaku
authors.initials: S
authors.lastname: Kashiwada
authors.forename: Kouichi
authors.initials: K
authors.lastname: Goka
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Shiraishi
authors.forename: Koji
authors.initials: K
authors.lastname: Arizono
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Ozato
authors.forename: Yuko
authors.initials: Y
authors.lastname: Wakamatsu
authors.forename: David E
authors.initials: DE
authors.lastname: Hinton
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis / Q000378:metabolism*; D004790:Enzyme Induction; D005260:Female; D005880:Gills / Q000201:enzymology* / Q000254:growth & development; D007814:Larva / Q000378:metabolism; D008099:Liver / Q000201:enzymology* / Q000254:growth & development; D008297:Male; D008748:Methylcholanthrene / Q000633:toxicity; D008856:Microscopy, Fluorescence; D009990:Oryzias / Q000378:metabolism*; D010078:Oxazines / Q000378:metabolism / Q000633:toxicity; D010084:Oxidation-Reduction
chemical_list: D010078:Oxazines; D008748:Methylcholanthrene; C007649:ethoxyresorufin; C014180:resorufin; D019363:Cytochrome P-450 CYP1A1