| The effects of non-polar environmental contaminants on components of the hypothalamo-pituitary adrenal (HPA) axis and the hypothalamo-pituitary-ovary (HPO) axis were examined in herring gull (Larus argentatus) embryos and cultured avian hepatocytes. In the HPA axis studies, regression analysis of herring gull embryo yolk sac organochlorine residues against basal plasma corticosterone concentrations indicated statistically significant inverse relationships for polychlorinated dibenzodioxins/polychlorinated dibenzofurans (PCDDs/PCDFs), total polychlorinated biphenyls (PCBs), non-ortho PCBs, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents (TEQs). The activities of two intermediary metabolic enzymes were inversely correlated with PCDDs/PCDFs. In a second study, high incidences of early onset of hatching were observed for herring gull eggs collected from some Great Lakes sites. Embryos from Scotch Bonnet Island were observed to have higher than average renal PEPCK activities and lower than average corticosterone stress responses. Regression analysis of embryo yolk sac organochlorine residues from three Great Lakes sites indicated a statistically significant positive relationship for basal plasma corticosterone concentrations and chlorinated hydrocarbons (CHCs), including organochlorine pesticides.; HPO axis studies involved development of a reverse-transcription-polymerase chain reaction (RT-PCR) bioassay to semi-quantitatively measure mRNA for the estrogen-inducible egg yolk precursor protein, vitellogenin (VTG), in avian embryo hepatocyte cultures. Short regions of VTG, β-actin and albumin cDNAs were cloned and sequenced for several species of birds. Hepatocyte cultures were prepared from both chicken and herring gull embryos and treated with the estradiol analogue, moxestrol, or the organochlorine insecticide, o,p′-DDT. Herring gull embryo hepatocyte cultures responded with VTG mRNA induction at 1 nM moxestrol, compared with 10 nM for chicken embryo hepatocyte cultures. Both herring gull and chicken embryo hepatocyte cultures responded with significant VTG mRNA induction when treated with 10000 nM o,p′-DDT. In chicken embryo hepatocyte cultures, 4-tert-octylphenol (OP) was determined to be very weakly estrogenic, whereas TCDD, benzo[k]fluoranthene (B[k]F), three halogenated dimethyl bipyrroles (HDBPs) and an extract prepared from a common tern ( Sterna hirundo) egg were determined to be anti-estrogenic. These results indicate that the semi-quantitative avian RT-PCR VTG mRNA bioassay may be useful for predicting whether wild birds may be sensitive (or exposed) to estrogenic or anti-estrogenic environmental contaminants. |
