Influences of sex steroids on experimental carcinogenesis

Sex steroids can apparently modify hepatic function in at least two ways (Figure 1). First, the liver contains specific receptor proteins for either androgens or oestrogens. Several studies, using effects on the monooxygenase system as an indicator of hormone action, have shown good correlations between the presence of sex-steroid receptors and hepatic response to these hormones. In general, androgens induce the activities of drug biotransformation reactions, whereas oestrogens depress them. Second, the endocrine milieu, during a critical period of early development, apparently programmes the hypothalamic-pituitary axis to release factors which cause certain aspects of liver biochemistry to undergo sex differentiation. Selected components of the cytochrome P-450 system exhibit sex differences, and these differences are imprinted by neonatal androgens and are initiated and maintained by the pituitary gland. Corresponding to sex differentiation of the hepatic monooxygenase system are significant sex differences in responses to hepatocarcinogens such as N-2-fluorenylacetamide and N-hydroxy-N-2-fluorenylacetamide. Higher incidences of hepatocellular carcinomas in males appear to result from exposure to neonatal androgens.