Evidence for a PCN-P450 enzyme in chickens and comparison of its development with that of other phenobarbital-inducible forms.

Of four monoclonal antibodies to purified rat liver cytochrome P450s, including those from 3-methylcholanthrene-, phenobarbital-, ethanol-, and pregnenolone-16-alpha-carbonitrile-treated rats, only the monoclonal antibody against pregnenolone-16-alpha-carbonitrile-inducible P450 immunodetected proteins in chicken liver microsomes after blotting from sodium dodecyl sulfate-polyacrylamide gels. This protein migrated identically with the pregnenolone-16-alpha-carbonitrile-inducible P450 detected in microsomes from dexamethasone-treated rats. It was most predominant in liver microsomes from chickens at 1 day posthatching, whereas much lower levels were observed in the embryo and at 36 days posthatch. Phenobarbital and dexamethasone were both effective inducers of this protein. The developmental profile and induction by phenobarbital and dexamethasone of several cytochrome P450-associated catalytic activities were compared with those of the immunodetected protein. Chicken liver microsomal erythromycin demethylase, a characteristic activity of rat pregnenolone-16-alpha-carbonitrile-inducible P450, was similar in developmental profile and induction to the immunodetected protein, with a high degree of augmentation at 1 day posthatch compared with that in the embryo and at 36 days posthatch; aldrin epoxidase, benzphetamine demethylase, ethylmorphine demethylase, and aminopyrine demethylase were more similar to each other in development and induction and were less well correlated with the immunodetected protein. This evidence suggests the presence in chicken liver of at least two types of P450, one a form related to the pregnenolone-16-alpha-carbonitrile-inducible P450 family. All of the catalytic activities were induced after pretreatment of chickens with phenobarbital but aldrin epoxidase was most effectively induced. Aldrin epoxidase was also detected in microsomes from untreated embryos as early as 7 days of incubation. Erythromycin demethylase was the only catalytic activity induced by dexamethasone. There was a trend of increased specific activity toward all the substances after hatching, indicating a more efficient P450 system, possibly due to a sharp increase in some isozymes, including the form from the pregnenolone-16-alpha-carbonitrile-inducible P450 family. This evidence for a pregnenolone-16-alpha-carbonitrile-inducible P450 in chickens agrees with sequence information that suggests the early evolution of this form and demonstrates the suitability of the chicken for studies of P450 evolution.