Neonatal administration of o , p '-DDT [1,1,1-trichloro-2-( o -chlorophenyl-2- p -chlorophenyl ethane or methoxychlor resulted in elevated levels of sex-differentiated hepatic monoamine oxidase activities in adult rats, but not in prepubertal animals. Exposure to these hormonally active xenobiotics may have changed the brain hormone environment during the critical period of development, resulting in endocrine alterations that were reflected by latent but permanent increases in hepatic monoamine oxidase activities, i.e. “altered imprinting”. Hepatic glutathione S -transferases and cytochrome P-450 content also underwent sex differentiation, but neonatal treatment with o , p '-DDT or methoxychlor did not alter levels in adult rats. However, glutathione S -transferase activities and cytochrome P-450 content were higher in prepubertal animals treated neonatally with o , p '-DDT. In contrast to monoamine oxidase, effects on glutathione S -transferase activities and cytochrome P-450 content were attributed to induction by these xenobiotics.
