Induction of in vitro EROD activity and in vivo caffeine metabolism in two species of New Zealand birds

In birds, induction of cytochrome P4501A (CYP1A) is usually assessed as liver microsomal ethoxyresorufin O-deethylase (EROD) activity, but in mammals, it can be determined by a caffeine metabolism blood test. We investigated both of these measures in two species of New Zealand birds. Administration of a model CYP1A inducer, β-naphthoflavone (BNF) (80 mg/kg i.p. twice 2 days apart), to paradise shelducks (Tadorna variegata; herbivore) and southern black-backed gulls (Larus dominicanus; omnivore) (n = 5 or 6) caused marked increases in EROD activity (80- and 20-fold, respectively). In both species, BNF treatment also caused significant increases (>8-fold) in caffeine metabolism determined prior to sacrifice as the serum concentration ratio of the major metabolite, paraxanthine, to caffeine, after caffeine administration (1 mg/kg i.p.). The results suggest in vivo caffeine metabolism is a potentially useful non-destructive biomarker of CYP1A induction in wild birds.