[Study on the water intake of rat during long-term inhalation of diesel exhaust]

To determine the chronic toxicity of diesel exhaust, F 344 rats were made to inhale various dilutions of exhaust under specific pathogen-free conditions for 16 hours a day, 6 days a week for 30 months. Five experimental groups of 240 rats each were set up, each consisting of equal numbers of rats of the both sexes of five weeks-old. During the experiment, they were housed in inhalation chambers, which were maintained at 23 +/- 2 degrees C and 55 +/- 10% relative humidity with artificial lighting 12 hours a day. Daily water intakes of all rats in inhalation chambers during the period of flow of fresh air with lights on and the period of inhalation of exhaust with lights off were measured with a drip meter fitted to automatic watering system in each inhalation chamber throughout the experiment. Result was that the mean daily water intake of the 0.5 mg/m3 (lowest particulate concentration level), 1.0 mg/m3, 1.8 mg/m3, and 3.7 mg/m3 (highest particulate concentration level) groups were 15%, 24%, 27%, and 39% less than that of the control group. Moreover, the groups also showed dose-dependent decrease in hourly water intake during the period of inhalation of diesel exhaust with lights off and dose-dependent increase in that during the period of flow of fresh air with lights on. This finding suggested that diesel exhaust might affect the circadian rhythm of the water intake in rats. These results showed that the measurement of the water intake of rat is an useful parameter to detect the biological effect on inhalation experiment.