In vitro/in vivo effects of 7,8-benzoflavone on aryl hydrocarbon hydroxylase activity of mice.

The activity of aryl hydrocarbon hydroxylase (AHH) in mouse liver microsomes was assayed in vitro in the presence of 7,8-benzoflavone (7,8-BF). The mice had been previously treated with the AHH inducer 3-methylcholanthrene (MC), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or vehicle (olive oil) alone. The effects of 7,8-BF on the AHH activity were markedly different according to the genetic responsiveness of the mice towards aromatic hydrocarbons (Ah). 7,8-BF had either an inhibitory or an enhancing effect on AHH, depending on the Ah responsiveness and previous treatment with MC or TCDD. In contrast, a single administration of 7,8-BF induced microsomal AHH, but the effect was much lower than MC or TCDD in both strains of mice. Simultaneous treatment or pre-treatment with 7,8-BF produced an inhibitory effect on AHH induction by MC or TCDD. Post-treatment with 7,8-BF inclined to promote the induction of AHH by MC or TCDD. These results suggest that the inhibitory effect of 7,8-BF is more exaggerated in vitro than in vivo. Inhibitory effects would be limited to AHH induction from MC or TCDD in in vitro studies, while they would depend on the time of application or Ah responsiveness in studies in vitro.