UPTAKE OF WATERBORNE 3,3',4,4'-TETRACHLOROBIPHENYL AND ORGAN AND CELL-SPECIFIC INDUCTION OF CYTOCHROME P4501A IN ADULT AND LARVAL FATHEAD MINNOW PIMEPHALES-PROMELAS

Female fathead minnows (Pimephales promelas) were exposed to water-bor ne [C-14]-3,3',4,4-tetrachlorobiphenyl (TCB) on days 0 and 5, for 24 h each time, in water with 0, 0.29, 2.9 or 29 mg TCB/kg total fish mass . Between treatments, fish were kept in clean water with normal feedin g and light conditions. Liver, ovary and skeletal muscle were collecte d at 2 h, on day 5 prior to the second dosing and on day 12. Initially , TCB uptake was greatest in liver, but after 5 days the content in ov aries (ca. 5 mug TCB/g wet weight) was similar to that in liver (ca. 4 mug/g wet weight). TCB concentration in muscle was 10% of that in liv er or ovary. Tissue concentrations of TCB were similar at 5 days after the first dose and 6 days after the second dose. Immunoblot analysis with monoclonal antibody 1-12-3 (specific for cytochromes P4501A; CYP1 A) showed that CYP1A content in liver homogenates increased with incre asing content of TCB in the liver, to about 5 pmol scup CYP1A equivale nts per mg protein at 1.8 mug TCB/g liver. Between 1.8 and 4 mug TCB/g liver, the CYP1A content increased another 10-fold. Ethoxyresorufin 0 -deethylase (EROD) activity in liver homogenates also increased with i ncreasing content of TCB in liver. However, EROD activity was suppress ed at TCB concentrations greater than 1.8 mug TCB/g liver, consistent with other results showing that 3,3',4,4'-TCB can inhibit or inactivat e CYP1A. Immunohistochemical staining with MAb 1-12-3 showed induction in liver and in multiple extrahepatic organs; analysis with a second anti-scup CYP1A1 MAb (1-71-3) confirmed the patterns of induction. A s trong CYP1A staining signal was detectable only in the highest dose gr oup, and induction in epithelial cells, including hepatocytes, was wea ker than that in endothelium. This suggests that the CYP1A seen in imm unoblots of liver homogenates could reflect a substantial contribution from endothelial cell P450. There was mild staining indicating CYP1A induction in endothelium of embryos hatched from eggs of exposed fish. Analysis of induction in fathead minnows is relevant to their use in evaluating chemicals that may be activated or detoxified by CYP1A enzy mes. The results further illustrate the utility of immunohistochemistr y to evaluate CYP1A induction as a marker of exposure.