Influence of estradiol on the benzo(a)pyrene hydroxylase activity induced by hexachlorocyclohexane

Basal BP-hydroxylase activity was measured in male Swiss mice from the age of 3 weeks to 20 months. Maximal enzyme activity was at the age of 5 months. Comparison of the inducibility of BP-hydroxylase by HCH was also investigated in male and female mice of different ages. Male mice showed higher induction of BP-hydroxylase by HCH than females of the same ages. Sterilization of female mice enhanced enzyme induction. Estradiol exhibited competitive inhibition of BP-hydroxylase activity. After treatment with HCH for 8 months, female mice had a lower tumour incidence than males, and this paralleled a lower induction of BP-hydroxylase.