Aryl hydrocarbon hydroxylase activity in human placenta from cigarette smoking and nonsmoking women.

Microsomal aryl hydrocarbon hydroxylase 4 is known to be present and inducible by polycyclic hydrocarbons in a variety of tissues of many species in vivo (5, 6, 12, 38, 40-43), in explants of rat lung in organ culture (42), and in mammalian cell cultures (24, 25). 5,6 This enzyme system may be important in understanding carcinogenesis, drug action, and steroid metabolism (4, 10). Polycyclic hydrocarbons are present as environmental or food contaminants as well as in cigarette smoke and are commonly ingested and inhaled by the human population. Some of the cancer incidence in humans