Abstract
These studies investigated the association ofcommon environmental contaminants 2,3,7,8‐tetraclorodibenzo‐ p‐dioxin (TCDD) and benzo[a]pyrene (B[a]P) with the yolk‐precursor protein vitellogenin (VTG). In vitro studies with purified VTG from the channel catfish (Ictaluruspunctatus) demonstrated that ^3^H‐TCDD and ^3^H‐ B[a]P associated with VTG in a nonsaturable manner. The magnitude of this association (i.e., pmoles of radioligand/mg VTG) increased with increasing chemical concentrations until the point of chemical insolubility in the incubation medium. In vivo, time‐course experiments with gravid female mummichogs (Fundulus heteroclitus) exposed to either ^3^H‐TCDD or ^14^C‐B[a]P revealed time‐ and dose‐dependent changes in total serum radiochemical content. In sera from female F. heteroclitus exposed to either chemical, >80%of detected radioactivity was associated with VTG and a second chromatographic peak, a lipoprotein fraction putatively identified as high‐density lipoproteins. In experiments comparing radiochemical serum compartmentalization in estrogenized (E2+) versus control male fish, the presence of VTG in E2 + males significantly altered the overall quantity and profile of serum protein‐associated radiochemical. In these experiments, serum VTG was present in very large quantities (40‐50% of total serum protein) and the majority (62‐81% for ^3^H‐TCDD; 56‐71% for ^14^C‐B[a]P) of radiolabeled ligand was associated with VTG. The structure of the VTG protein, combined with the apparently nonsaturable nature of the association between VTG and these lipophilic compounds, suggests a VTG‐ligand association that is both nonspecific and of significant capacity. Given the central role of VTG in egg production and early‐life development, these findings suggest a significant role for VTG as a vector of xenobiotic maternal transfer. This role is further supported by companion studies (this volume) that examined oocyte accumulation of TCDD and B[a]P.