STUDIES ON THE RELATIVE INSENSITIVITY OF THE IMMATURE RAT TO THE NEUROTOXIC EFFECTS OF 1,1,1-TRICHLORO-2,2-BIS(p-CHLOROPHENYL) ETHANE (DDT)

¹ Departments of Environmental Toxicology and Animal Physiology, University of California, Davis, California

The LD5O for 1, 1, 1-trichloro-2,2-bis(p-chlorophenyl) ethane (DDT) was found to be 728 mg kg for the 10-day old rat and 250 mg/kg for the 60-day-old rat, in agreement with a previous report that the immature rat is less sensitive than the adult to the effects of DDT. In order to explain this nearly 3-fold difference in toxicity, the relative abilities of the 10-and 60-day-old rat to absorb, distribute and metabolize DDT were compared by analyzing brain, spinal cord, liver and plasma for DDT and its principal metabolites, 1, 1-dichloro-2,2-bis(p-chlorophenyl) ethane (DDD) and 1, 1-dichloro-2,2-bis(-chlorophenyl) ethylene (DDE), at various timeintervals after p.o. administration of 100 mg/kg of DDT. Also, brain concentrations of DDT required to produce death were determined in the two age groups after administration of lethal doses. It was concluded that the greater dose of DDT required for toxic effects in the young rat is due to two factors : 1) higher brain concentrations of DDT are required to produce death in the young rat, thus indicating that the brain of the 10-day-old rat is less sensitive to DDT than is the brain of the adult rat; 2) the central nervous system of the young rat is less efficient in clearing plasma of DDT. This may be due to the lower lipid levels of the central nervous system of the young rat and to the high lipid solubility of DDT.