Evidence that paraquat is able to cross the blood-brain barrier to a different extent in rats of various age.

The brain levels of paraquat were determined in rats of different age after systemic administration of several doses of the herbicide. Two week-, 3, 12 and 24 month-old rats were subcutaneously injected with paraquat (1, 2.5 and 5 mg/kg) and sacrificed 1 h later. A method based on ion-pair solid-phase extraction and reversed-phase high performance liquid chromatography was used to measure brain paraquat concentrations. The acute administration of paraquat resulted in dose-related and age-dependent brain concentrations of the herbicide, higher brain levels being detected in 12 and 24 month-old rats in comparison to young animals (3 month-old). In comparison with 3 month-old rats, higher concentrations of paraquat were also observed in the brain of 2 week-old animals. The present results demonstrate that in rats systemic treatment with paraquat gives rise to higher brain concentrations of this herbicide in very young and old rats in comparison with 3-month-old animals. This suggests that age-dependent changes in blood brain barrier permeability may account for these differences.