Neurotoxicity and metabolism of methyl bromide in rats

Abstract

Changes in locomotor activity, body temperature, and body weight gain, and the enhancement of thiopental-induced sleep were investigated inrats as indices of the functional changes in the CNS caused by methyl bromide (CH 3Br) exposure. The correlations of these behavioral changes with CH 3Br metabolism are discussed. The LC50 value and its 95% confidence limits for an 8-hr exposure of CH 3Br was 302 ppm (267–340) ppm. Effects were examined following exposure to 63, 125, 188, or 250 ppm CH 3Br for 8 hr. CH 3Br concentrations as low as 63 ppm remarkably enhanced the sleep-inducing potency of thiopental, but CH 3Br exerted no effect on thiopental metabolism. The body temperature and body weight gain were decreased at exposure to concentrations of 125 ppm or higher, and locomotor activity was reduced at 188 ppm or higher. These effects were reversible and, at 24 hr after the exposure, locomotor activity and body temperature were almost the same as in control rats. In a time-course study of CH 3Br, bromine, and methyl alcohol, CH 3Br was rapidly eliminated from rat tissues following the cessation of exposure, with a half-life of about 30 min in the early post-exposure period. In contrast, the elimination rate of bromine was very slow, with a half-life about 5 days. The methanol amount was below that reported to induce the changes in CNS functions. These results suggest that the CNS depression caused by CH 3Br exposure may be due to the CH 3Br molecule or the methyl moiety incorporated into tissues and may not be attribuatable to bromine or methanol. A linear relationship was obtained between bromine amounts in blood and the exposure concentration or duration. This result suggests the possibility that the extent of CH 3Br exposure may be estimated from the bromine quantities in blood.