title: Reduction of cytochrome P4501A with age in Atlantic tomcod from the St. Lawrence Estuary, Canada: relationship with emaciation and possible effect of contamination.
abstract: This study reports a reduction of ethoxyresorufin-O-deethylase (EROD) activity in large-sized, older Atlantic tomcod (Microgadus tomcod) collected in the St. Lawrence Estuary (Quebec, Canada) and investigates its relationship over a 4-year period to sex, gonadosomatic index (GSI), condition factor (CF) and cytochrome P4501A (CYP1A) mRNA levels. In addition, the concentrations of polychlorinated biphenyls (PCBs) were measured in a subsample of fish. The reduction of EROD activity with age was observed each year in both sexes and was not related to the GSI. A high proportion of large-sized fish, with a body length greater or equal to 225 mm, were emaciated (CF < or = 0.55). A 6-16-fold reduction of EROD activity and a 2-4-fold reduction of CYP1A mRNA levels were observed in large-sized emaciated females compared to small-sized non-emaciated females. Concentrations of PCBs in liver increased from 1000 to 4000 ng/g lipid weight as the hepatic lipid content and the CF decreased. The inter-annual variation of EROD activity was associated with the variation in CF with lowest EROD activity and CF in 1999. When emaciated fish were excluded from the analyses, EROD activity was still lower (2-5-fold) in large compared to small fish and was no longer related to CF. For similar levels of CYP1A mRNA, EROD activity was lower in large compared to small fish. Thus, there was post-transcriptional inhibition of CYP1A activity in large-sized tomcod, indicative of cellular dysfunction. This response may be related to aging, chronic exposure to toxic contaminants or to selective pressures favoring less responsive individuals. This study demonstrates that fish age, size, and CF are important variables to consider in studies using EROD activity as an indicator of environmental contamination. The main finding was that a large part of the reduction of CYP1A with age in St. Lawrence Estuary tomcod was associated with severe emaciation of a large proportion of large-sized fish. Hepatic concentrations of contaminants covaried with the CF and the effects of these two variables on CYP1A could not be discriminated.
authors.affiliation: Department of Fisheries and Oceans, Maurice Lamontagne Institute, 850 route de la mer, Mont-Joli, Qc, Canada G5H 3Z4. couillardc@dfo-mpo.gc.ca
authors.forename: C M
authors.initials: CM
authors.lastname: Couillard
authors.forename: I I
authors.initials: II
authors.lastname: Wirgin
authors.forename: M
authors.initials: M
authors.lastname: Lebeuf
authors.forename: B
authors.initials: B
authors.lastname: Légaré
mesh_terms: D000367:Age Factors; D000818:Animals; D001824:Body Constitution / Q000502:physiology*; D002170:Canada; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis* / Q000378:metabolism; D004614:Emaciation / Q000662:veterinary; D004794:Enzyme Repression; D005399:Fishes / Q000378:metabolism* / Q000502:physiology; D008099:Liver / Q000378:metabolism; D011078:Polychlorinated Biphenyls / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D012737:Sex Factors
chemical_list: D012333:RNA, Messenger; D011078:Polychlorinated Biphenyls; D019363:Cytochrome P-450 CYP1A1