IN-VITRO INDUCTION OF ETHOXYRES ORUFIN-O-DEETHYLASE AND PORPHYRINS BYHALOGENATED AROMATIC-HYDROCARBONS IN AVIAN PRIMARY HEPATOCYTES

Ethoxyresorufin-O-deethylase (EROD) and porphyrin induction responses of primary hepatocytes to halogenated aromatic hydrocarbons (HAHs) wer e examined in newly hatched domestic chickens, herring gulls, ring-bil led gulls, double-crested cormorants, and Forster's terns. Concentrati on-response relationships were determined for both biochemical respons es in hepatocyte preparations derived from individual avian livers (ex cept for the tern). The choice of vehicle used to dose chicken hepatoc ytes greatly affected the potencies and efficacies of HAHs. Dimethyl s ulfoxide resulted in median effective concentration (EC50) values for EROD induction that were between 10 and 15 times less than isooctane ( isooctane was used throughout the study). Neither vehicle induced EROD activity by itself. Concentration-dependent increases in EROD activit y were observed with several HAHs, and their potencies (EC50 values) w ere compared to that of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) wit hin each hepatocyte preparation to determine relative potency factors (RPFs). Differences in sensitivity to these responses were observed am ong individuals within each of the species and among species. Median E C50 values (nM) for EROD induction by TCDD were 0.72, 13, 20, 25, and 150 for the chicken, cormorant, ring-billed gull, herring gull, and te rn hatchling, respectively. Relative potency factors for several HAHs were different, in both ranking and potency, from those generally deri ved in mammalian hepatocytes. Porphyrin accumulation was observed occa sionally with the most potent aryl hydrocarbon receptor agonists, but most HAHs were not tested at concentrations sufficiently high to obser ve a consistent response. This study provides information on interindi vidual and interspecies differences in responsiveness to TCDD-like com pounds and provides species-specific RPFs that may prove useful for th e purpose of hazard and risk assessment for fish-eating birds.