INDUCTION OF ETHOXYRESORUFIN O-DEETHYLASE (EROD) AND ENDOTHELIAL ACTIVATION OF THE HETEROCYCLIC AMINE TRP-P-1 IN BIRD EMBRYO HEARTS

The xenobiotic-metabolizing activity of avian heart was investigated i n chicken and Elder duck embryos exposed to aryl hydrocarbon (Ah) rece ptor agonists in ovo. Both beta-naphthoflavone (BNF) and 3,3',4,4',5-p entachlorobiphenyl (PCB 126) induced 7-ethoxyresorufin O-deethylase (E ROD) activities in chicken embryo hearts whereas Elder duck embryos on ly responded to BNF. The differential responses of chicken and Elder d uck embryos were used to examine the involvement of Ah receptor-mediat ed enzyme induction in the activation of the environmental and food mu tagen 3-amino-1,4-dimethyl-5H-pyrido[4, 3-b]indole (Trp-P-1). As deter mined by light microscopic autoradiography, there was a highly selecti ve binding of non-extractable H-3-Trp-P-1-derived radioactivity in end othelial cells of large vessels and capillaries in hearts of BNF- and PCB 126-treated chicken embryos. No binding occurred at these sites in vehicle-treated controls. There was also a strong endothelial binding of H-3-Trp-P-1 in hearts of BNF-treated Elder duck embryos whereas no binding occurred in hearts of PCB 126-treated Elder duck embryos. A p ositive correlation between induction of EROD activity and covalent bi nding of H-3w-Trp-P-1 to protein in heart homogenates from BNF- and PC B 126-treated chicken and Elder duck embryos was also observed. The re sults suggest a cytochrome P450 1A (CYP1A)-mediated activation of Trp- P-1 in avian heart endothelial cells although involvement of other Ah receptor-regulated enzymes is also possible. We propose that heart end othelial cells may be targets for bioactivation and toxicity of enviro nmental contaminants in birds exposed to Ah receptor agonists.