Acquisition of aryl hydrocarbon hydroxylase inducibility by aromatic hydrocarbons in monolayer-cultured hepatocytes from nonresponsive mouse strains.

The expression of P1450 and P3450 genes isolated from C57BL26 mouse liver in mouse hepatocytes from responsive (BALB/c, C3H/He, C57BL/6, and CBA) and nonresponsive (AKR, DBA/2, NZB, and NZW) strains in primary culture after exposure to aromatic hydrocarbons was investigated with respect to aryl hydrocarbon hydroxylase (AHH) activity and corresponding P450 transcript levels. Constitutive AHH activity in all strains decreased with an increasing culture period. The AHH activity of cells treated with either benz(a)anthracene, benzo(a)pyrene, 3-methylcholanthrene, or TCDD continuously or 24 h before harvesting was measured during observation periods for up to 5 days. Slight induction of AHH activity by benz(a)anthracene, benzo(a)pyrene, and 3-methylcholanthrene was observed in hepatocytes from the CBA and C3H/He strains during the first half of the observation period, followed by a steep increase thereafter. Enzyme activities in hepatocytes from BALB/c mice were the same as or lower than the control values during the first half of the observation period, and in the C57BL/6 mouse high levels of AHH activities were observed even during this period. AHH activities in hepatocytes from the AKR, DBA/2, NZB, and NZW mice after treatment with aromatic hydrocarbons were lower than control levels during the first half of the observation period; however, significant induction was observed thereafter. P450 transcripts including both P1450 and P3450 RNA species were detected when the treatment was started during the early incubation period, whereas only P1450 RNA was found at the later periods. The amounts of P1450 transcript also correlated well with AHH activity, higher levels being found after starting treatment with benz(a)anthracene at day 3 or 4 than at day 1. Our observations indicate that, although AHH induction was genetically determined in each strain, activity can be induced in hepatocytes of so-called nonresponsive as well as responsive mouse strains by treatment with aromatic hydrocarbons after transfer of the cells to primary culture.