Tissue and sex differences in the activation of aromatic hydrocarbon hydroxylases in rats

Betamethasone and α-naphthoflavone produced similar activation of biphenyl 2-hydroxylase and benzoa]pyrene 3-hydroxylase in control male rat liver microsomes. In small intestinal epithelial microsomes, betamethasone had no effect whereas α-naphthoflavone caused a pronounced activation of benzoa]pyrene hydroxylation and a lesser activation of biphenyl 2-hydroxylation. In lung microsomes, betamethasone had no effect on either enzyme activity whereas α-naphthoflavone had no effect on biphenyl 2-hydroxylase but inhibited benzoa]pyrene hydroxylase. In kidney cortex microsomes from male rats both compounds caused inhibition or had no effect whereas in kidney cortex microsomes from female rats betamethasone activated whereas α-naphthoflavone had no effect.Activation also occurred in isolated viable hepatocytes from male rats. The response of biphenyl 2-hydroxylase was very similar to that found in male rat liver microsomes but benzoa]pyrene hydroxylase was more sensitive to activation and less sensitive to inhibition than in microsomes. The findings are interpreted as demonstrating the presence of more than one ‘latent’ aromatic hydrocarbon hydroxylase in rodents.