Comparison of blood and brain toluene concentrations and circulating triglyceride levels resulting from acute and repeated exposures in rats.

Male Sprague-Dawley rats were exposed by inhalation to 2500 ppm toluene three hours per day, five days per week for three weeks. Blood and brain toluene concentration and circulating triglyceride levels were measured after one day, one week, two weeks and three weeks exposure. A consistent reduction in mean body weight gain was found in the toluene-exposed rats compared to controls as early as three days following initiation of exposure. During the second and third exposure week, the toluene-exposed rats exhibited marked salivation during the exposure periods. A dramatic decrease in brain and blood toluene levels occurred between the second and third exposure weeks. Also, an inverse relationship between circulating triglyceride levels and blood and brain toluene concentrations was found in the exposed rats. Plausible mechanisms for tolerance development and the inverse relationship to circulating triglycerides are offered including induction of hepatic mixed function oxidase activity and alterations in brain biomembrane lipid composition.