Abstract
Studies of perinatal exposures to dioxin-like compounds (DLCs), coplanar polycyclic halogenated aromatics whose prototype is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), have employed a variety of outcome measures to investigate effects on the reproductive/developmental, endocrine, immune, and neurobehavioral systems. The effects include infertility, growth retardation, fetal loss, changed sexual differentiation, reduced cognitive/motor function, dermatologic and other ectodermal effects, and decreased immune response. Significant biomarkers have included sperm count; CD4/CD8 ratio; and levels of testosterone, T4, and dopamine. Using specific dioxin or PCB congeners, these and other markers were used to investigate the mechanisms of the observed effects. The DLCs, which include some PCB congeners, are characterized by high-affinity binding to the Ah receptor; most biological effects are thought to be mediated by the ligand-Ah receptor complex. Other PCB congeners have low affinity for the Ah receptor, and operate by non-Ah receptor mechanisms. The biologic activity of a PCB mixture is the sum of the agonist and antagonist activities of the different constituents in the mixture. Animal studies with specific PCB congeners can help to clarify these activities. With similar approaches, biologic markers of effect can be developed and applied in epidemiologic studies to monitor for, and predict, adverse effects in humans.