Six-month-old lesser scaup (Aythya
affinis) and nestling tree swallows (Tachycineta bicolor) were injected intraperitoneally with
beta-naphthoflavone (BNF) in
corn oil or in vehicle alone. Liver samples were taken and stored at -80 degrees C until microsome preparation and
monooxygenase assay. Skin samples were placed in buffered
formalin for subsequent immunohistochemical (IHC) analysis for
cytochrome P4501A (CYP1A). Lesser scaup treated with BNF at 20 or 100 mg/kg
body weight showed approximately 6- to 18-fold increases in four
monooxygenases (
benzyloxyresorufin-O-dealkylase,
ethoxyresorufin-O-dealkylase, methoxyresorufin-O-dealkylase, and
pentoxyresorufin-O-dealkylase). No IHC response was observed for CYP1A in the skin of vehicle-injected ducks, whereas in the skin from BNF-treated ducks, the positive IHC response was of similar magnitude for both dose levels of BNF. Tree swallows injected with BNF at 100 mg/kg, but not at 20 mg/kg, showed significant increases (approximately fivefold) in hepatic microsomal O-dealkylase activities.
Cytochrome P4501A was undetectable by IHC response in skin from
corn oil-treated swallows, but positive IHC responses were observed in the skin of one of five swallows at 20 mg/kg and four of five swallows at 100 mg/kg. Although these data do not allow construction of significant dose-response curves, the IHC responses for CYP1A in skin support the possible use of this nonlethal approach for biomonitoring contaminant exposure of birds. In addition, the CYP1A signal observed at the bases of emerging feathers suggest that these might provide less invasive sampling sites for IHC analysis of CYP1A.