Enzyme induction of the early chick embryo by airborne particulate extracts

The induction by airborne particulate extracts of aryl hydrocarbon hydroxylase (AHH) and 7-ethoxycoumarin O-deethylase (ECOD) in early chick embryos was studied to determine whether or not lethality by the extracts was related to the induction. The optimal pH values for AHH and ECOD were 7.1 and 6.9, respectively, after administering the extracts to early embryos. The AHH inducing capacity was significantly increased 4 h after injection of the extracts, then the value gradually increased. The ECOD inducing ability was similar to that of AHH, although to a lesser extent. Among fractions from the extracts, the neutral fraction was responsible for most of the AHH inducing activity. Two neutral subfractions (N2 and N3), consisting mostly of polycyclic aromatic hydrocarbons (PAH) and their derivatives, had the highest inducing activity. A dose-response relationship was observed between the amounts of the N2 and induction of AHH and ECOD in 8-day-old embryos. When the N2 was administered at different stages of development (days 5-9), the values of induced AHH and ECOD activities increased along with the days of development. Extracts of the smaller airborne particulates (< 1.1 and 1.1-2.0 microns cut-off diameters) had stronger AHH and ECOD inducing abilities than those of the larger, since the former contained high levels of PAH and their derivatives. These results suggested that PAH and their derivatives in the airborne particulates induced AHH and ECOD activities in the early chick embryo. The relationship between the extent of AHH and ECOD inducing activities and that of embryolethality caused by extracts of airborne particulates was not well established.