IMPACT OF CHLORINATED DIOXINS AND FURANS ON JAPANESE QUAIL, RING- NECKED PHEASANT, AND DOMESTIC CHICKEN: INSIGHTS FROM IN OVO STUDIES

摘要

Dioxin-like compounds (DLCs) act via the aryl-hydrocarbon receptor (AhR) to stimulate expression of biotransformation enzymes, including cytochrome P450 1A4 (CYP1A4) in birds. Based on available toxicity data and the amino acid sequence of the AhR ligand binding domain (LBD) of more than seventy avian species, species can be classified as Type 1 (very sensitive), Type 2 (moderately sensitive) or Type 3 (insensitive). To further investigate this species-sensitivity classification scheme we performed a series of egg injection studies using Japanese quail (Coturnix japonica; Type 3), ring-necked pheasant (Phasianus colchicus; Type 2), and chicken (Gallus gallus; Type 1). Eggs from each species were exposed to various doses of 2,3,7,8-tetrachlorodibenzo-p-doxin (TCDD), 2, 3, 7, 8-tetrachlorodibenzofuran (TCDF) or 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) via injection into the air cell. Liver tissue was collected 10-d post-hatch for analysis of CYP1A4 mRNA abundance by real-time PCR (qPCR). Results indicate that TCDD, PeCDF and TCDF differ in their CYP1A4 inducing potential, both within and across species. Assuming CYP1A4 transcript abundance can be used as a measure of sensitivity, chicken is the most sensitive species followed by ring-necked pheasant and Japanese quail. Results also demonstrated that PeCDF, and not TCDD, was the most potent DLC in pheasant, but not in quail and chicken.