Effects of xenoestrogen treatment on zona radiata protein and vitellogeninexpression in Atlantic salmon (Salmo salar)

Zonagenesis (zonar radiata protein synthesis) and vitellogenesis (yolk prot ein synthesis) are two reproductive responses that are integral aspects of fish oogenesis. This study examines the responses of eggshell zona radiata proteins (Zrp) and vitellogenin (Vtg) to five environmental pollutants; 4-n onylphenol (NP) and o,p'-DDT [both at 25 mg/kg], lindane (gamma-HCH) [10 mg /kg], a technical PCB mixture (Aroclor 1254; A1254) and bisphenol A (BPA) [ both at 5 mg/kg] in juvenile Atlantic salmon (Salmo salar). Fish were given intraperitoneal injections of o,p'-DDT, gamma-HCH, A1254 or BPA; singly, i n combination with NP, and as a cocktail of all five chemicals, and later c ompared to NP-treated and untreated fish. In a separate experiment, fish we re exposed to BPA in a dose-response manner (1, 5, 25 and 125 mg/kg fish). Based on previous studies, blood and liver samples were collected 2 weeks a fter injection. Zrp and Vtg levels were analyzed in plasma using immunoblot ting and enzyme-linked immunosorbent assay. Liver cytochrome P4501A was ana lyzed by 7-ethoxyresorufin O-deethylase (EROD) activity. NP caused pronounc ed elevations in plasma Zip and Vtg levels. In comparison, when NP was give n in combination with gamma-HCH, Vtg levels was significantly reduced, comp ared to NP treatment alone. Using o,p'-DDT, A1254 and BPA, significant elev ations of plasma Zrp and Vtg were seen when chemicals were given in combina tion with NP, but not when administered by themselves. An apparent dose-res ponse induction of Vtg and Zrp levels were observed in BPA treated juvenile salmon. In immunoblots, one component of molecular weight approximating th e Zrp-beta was detected when either o,p'-DDT, gamma-HCH, A1254 or BPA were given singly. A1254 significantly induced hepatic EROD activity when admini stered alone. However, when given as a mixture with all the other xenobioti cs, reduction of EROD activity was observed. The data suggest a pattern of xenobiotics action which may complicate assessment of their reproductive ef fects. Zrp (the beta monomer) was more responsive to the xenoestrogens than Vtg, and provides a sensitive means of detecting exposure to environmental estrogens. (C) 2000 Elsevier Science B.V. All rights reserved.