Abstract
The toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD] and its congeners involves binding to a specific TCDD [Ah] receptor, interaction of this complex with chromatin, and the ultimate production of pleiotropic responses. The mechanism whereby these effects are produced following interaction of TCDD with the receptor complex is not known. Oxidative stress following the production of reactive oxygen species (ROS) may play an important role in the toxic manifestations of TCDD. Thus, the dose and time-dependent effects of TCDD on the production of superoxide anion by peritoneal lavage cells (primarily macrophages) from rats were examined. A maximum increase in superoxide anion production occurred on day 1 after treatment in rats with 50 and 125 μg TCDD/kg. At 6 h after a single dose of 125 μg TCDD/kg, a 2.4-fold increase in superoxide anion production was observed in peritoneal lavage cells from rats. A single dose of 5 μg TCDD/kg had no effect on superoxide anion production by peritoneal lavage cells. A significant increase in DNA single strand breaks within peritoneal lavage cells occurred at 12 h after the oral administration of 50 μg TCDD/kg, and a maximum increase in DNA single strand breaks was observed on days 3-5 after treatment. No DNA damage was detected at a dose of 5 μg TCDD/kg. No difference was observed with respect to dose and time in the composition of the peritoneal lavage cells. The results clearly indicate that the oral administration of TCDD activates peritoneal lavage cells in rats, and that the activation precedes the formation of DNA single strand breaks. The results support the hypothesis that the tissue damage by TCDD may be due, at least in part, to the formation of reactive oxygen species, and macrophages may serve as one source of reactive oxygen species in response to TCDD.