An evaluation of the etiology of reduced CYP1A1 messenger RNA expression in the Atlantic tomcod from the Hudson River, New York, USA, using reverse transcriptase polymerase chain reaction analysis

Adult Atlantic tomcod, Microgadus tomcod, from the Hudson River, New York S tate, USA, exhibit reduced inducibility of hepatic cytochrome P4501A1 (CYP1 A1) mRNA compared with adult tomcod from the cleaner Miramichi River, New B runswick, Canada, when treated with coplanar polychlorinated biphenyl (PCB) congeners or 2,3,7,8-tetrachlorodibenzo-p-dioxin. In contrast, little. dif ference in CYP1A1 inducibility is observed between tomcod from these two ri vers when treated with polycyclic aromatic hydrocarbons (PAHs). We sought t o determine if impaired hepatic CYP1A1 inducibility in Hudson River tomcod results from a multigenerational, genetic adaptation or a single generation al, physiological acclimation. Embryos and larvae from controlled experimen tal crosses of Hudson River and Miramichi River parents were exposed for 24 h to water-borne PCB congener 77 (10 ppm), benzo[a]pyrene (BaP; 10 ppm), o r dimethysulfoxide, and CYP1A1 expression was assessed in individual larva using competitive reverse transcriptase polymerase chain reaction (RT-PCR) analysis. The CYP1A1 mRNA was significantly induced in larvae from both pop ulations by BaP (47- and 52-fold) and PCB 77 (9- and 22-fold), although lev els of expression were higher in offspring of Miramichi matings. Most impor tant, CYP1A1 mRNA was significantly induced by PCB 77 in larvae from Hudson River parents. Concentrations of dioxin, furan, and PCB congeners were mea sured in livers and eggs of female tomcod from these two locales to quantif y the extent of maternal transfer of contaminants. For both rivers, wet-wei ght contaminant concentrations were significantly higher (4-7 times) in liv ers than in eggs of the same females, suggesting that a threshold level of contaminants may have to be reached before CYP1A1 transcription is impaired . We conclude that reduced inducibility of hepatic CYP1A1 mRNA in adult tom cod from the Hudson River is most consistent with single-generational accli mation.