Pulmonary effects of repeated exposures to paraquat aerosol in guinea pigs.

Exposure to paraquat, a widely used herbicide, has been shown to produce a concentration dependent rapid, shallow breathing pattern in guinea pigs 18 hr following exposure (H. Burleigh-Flayer and Y. Alarie, 1987, Arch. Toxicol. 59(6), 391-396). To further explore the pulmonary effects following exposure to paraquat, two experiments were carried out. The first experiment consisted of exposing a group of guinea pigs for a period of 4 hr to 0.7 mg/m3 paraquat aerosol and monitoring respiratory variables for 2 weeks following the exposure. In the second experiment, three groups of guinea pigs were repeatedly exposed to three concentrations of paraquat aerosol (0.1, 0.4, and 0.8 mg/m3) for 6 hr a day, 5 days a week for 3 weeks. Respiratory variables were measured each day of these 3-week experiments. The respiratory variables evaluated in both experiments were tidal volume (VT) and respiratory frequency (f). These variables were monitored during air breathing and upon challenge with 10% CO2 in 20% O2 and 70% N2 in order to evaluate the pulmonary effects of exposure to paraquat. Following a single exposure to 0.7 mg/m3 paraquat aerosol, a decrease in VT and increase in f were seen during air and 10% CO2 challenge which reached a maximum several days following exposure. After reaching maximal changes, the respiratory variables returned to control values. With repeated 6-hr exposures to paraquat aerosol, guinea pigs exposed to 0.4 and 0.8 mg/m3 also displayed a rapid, shallow breathing pattern. Adaptation to the exposures for these two concentration groups was evidenced by a return of the respiratory variables toward control levels. This adaptation typically occurred during the first 7 days of exposures. A cumulative effect was therefore not detected with repeated exposures to paraquat aerosols.