Effect of subchronic inhalation exposure to low-level trichloroethylene on heart rate and wakefulness-sleep in freely moving rats.

Electroencephalographic (EEG) and heart rate (HR) responses to repeated 8-h exposure for 6 weeks to trichloroethylene (TRI) vapor of 50, 100 and 300 ppm were examined in freely moving rats with chronically implanted electrodes for polygraphic recordings. Exposure to all the TRI levels significantly decreased amount of time spent in wakefulness (W) during the exposure period. Exposure to 100 ppm and higher levels significantly decreased the time-averaged HR during the post-exposure period. The HRs during the stages of slow-wave sleep (SWS) and paradoxical sleep (PS) were significantly lowered after cessation of exposure to 50 ppm. When compared with the previously reported responses to short-term exposure to TRI (Arito H, et al. Arch Toxicol 1993; 67: 193-199), significant changes in wakefulness-sleep and HR elicited by the long-term exposure appeared at lower exposure levels. The EEG and HR effects of long-term exposure to TRI of 50 ppm or higher levels are discussed for their causative factors on the basis of the reported findings and for validity of the ongoing biological exposure limit value of TRI with reference to documentations enlisted for ACGIH's TLV of 50 ppm (ACGIH. Documentation of the threshold limit values and biological exposure indices, 5th ed. 1986: 595-597).