Induction of CYP1A mRNA and catalytic activity in gizzard shad (Dorosoma cepedianum) after waterborne exposure to benzo[a]pyrene.

The purpose of this study was to examine the concentration and time-dependent response of hepatic CYP1A mRNA levels and ethoxyresorufin O-deethylase (EROD) activity in gizzard shad (Dorosoma cepedianum) after waterborne exposure to the polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP). Gizzard shad hepatic CYP1A mRNA levels and EROD activity were increased within 6 hr by waterborne concentrations of 1.01 microgram BaP/l and were highest after 72 hr of exposure. The median effective time to reach 50% of maximum induction (ET50) values for CYP1A mRNA and EROD activity was 12 +/- 9 and 34 +/- 3 hr, respectively. The rise of CYP1A mRNA levels ahead of the rise of EROD activity showed that the CYP1A gene has the general pattern of a gene that is under transcriptional control. Although CYP1A mRNA levels were maximally induced after 72 hr of exposure, they returned to basal levels between 72 and 120 hr of exposure. Despite a decrease in CYP1A mRNA levels between 72 and 120 hr of exposure, EROD activity did not significantly change between 72 and 120 hr of exposure. These results indicate that hepatic CYP1A mRNA levels in gizzard shad can only feasibly identify short-term exposures to BaP concentrations of approximately 1 microgram/l and that are not longer than 72 hr. Consequently, hepatic CYP1A catalytic activity (e.g., EROD) and CYP1A protein levels should be measured in addition to hepatic CYP1A mRNA levels when biomonitoring aquatic systems for certain types of chemical contamination.